Rodak's Hematology: Clinical Principles and Applications, 5th Ed.

CHAPTER 36. Mature lymphoid neoplasms

Magdalena Czader

OUTLINE

Morphologic and Immunophenotypic Features of Normal Lymph Nodes

Cortex

Paracortex

Medulla

Sinuses

Lymph Node Processing

Reactive Lymphadenopathies

Follicular Pattern

Paracortical Pattern

Sinusoidal Pattern

Mixed Pattern

Lymphomas

Mature B Cell Lymphomas

Mature T Cell and Natural Killer Cell Lymphomas

Hodgkin Lymphoma

Objectives

After completion of this chapter, the reader will be able to:

1. Describe normal lymph node morphology and discuss the function of various compartments and constituent cells.

2. Outline the most common histologic patterns of reactive lymphadenopathies.

3. Describe the peripheral blood findings in chronic lymphocytic leukemia and hairy cell leukemia.

4. Describe the approach to the diagnosis of lymphomas as outlined by the World Health Organization classification.

5. Discuss the most commonly occurring mature B and T cell neoplasms, including epidemiology, clinical presentation, pathophysiology, lymph node histologic features, peripheral blood or bone marrow findings, and diagnostic test results.

6. Interpret diagnostic test results to identify lymphoproliferative disorders.

CASE STUDY

After studying the material in this chapter, the reader should be able to respond to the following case study:

A 46-year-old previously healthy man came for evaluation of an enlarged left cervical lymph node. The patient had discovered this isolated lymphadenopathy 2 weeks previously and did not complain of any other symptoms. The lymph node measured approximately 2 cm. The findings of his physical examination were otherwise unremarkable. The lymph node was excised, and microscopic examination showed the histologic features presented in Figure 36-1A. Immunohistochemical stains showed CD20 (Figure 36-1B), CD10, and BCL-6 positivity and focal CD30 antigen expression.

1. What is your diagnosis based on the histologic and immunophenotypic features?

2. What additional immunophenotypic features that confirm the diagnosis could be seen using flow cytometry?

3. Is it likely that this patient would show disseminated disease, including bone marrow involvement?

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FIGURE 36-1 Histologic lymph node findings for the patient in the case study. A, Lymph node (hematoxylin and eosin stain, ×500). B, CD20 antigen expression in the lymphoid population (immunoperoxidase stain, ×500).

Lymphomas are neoplasms of the lymphoid system. Original microscopic observations and immunophenotypic and molecular studies confirmed that these malignancies recapitulate specific stages of normal lymphoid differentiation. The diagnosis is based on a combination of biologic features such as morphology, immunophenotype and molecular genetic characteristics, and clinical information.1 Therefore, during initial sample processing, the appropriate steps must be taken to ensure tissue preservation and availability for microscopic examination and immunophenotypic and molecular studies.

Knowledge of normal lymphoid differentiation is a prerequisite for understanding the lymphoid neoplasms. This chapter describes the morphologic and immunophenotypic features of normal lymph nodes and selected common lymphomas and lymphoproliferative disorders. Reactive lymphoid hyperplasias, which can resemble lymphoid neoplasms, also are discussed.

Morphologic and immunophenotypic features of normal lymph nodes

Lymphoid organs serve as sites of antigen recognition, antigen processing, and lymphopoiesis. Most of the lymphoid tissue is concentrated in lymph nodes, which are round to oval encapsulated organs serving as primary sites of immunologic response. They are particularly prominent at sites with an environmental interface. Large groups of lymph nodes are found draining specific peripheral areas (e.g., cervical, axillary, or inguinal). Similarly, internal organs are served by regional lymph nodes (e.g., mediastinal, hilar, and mesenteric). Respiratory and digestive tracts have additional aggregates of lymphoid tissue located directly in the mucosa called mucosa-associated lymphoid tissue (MALT). These aggregates are the primary sites of antigenic contact and drain directly into regional lymph nodes.

Histologic components of a lymph node include cortex, paracortex, medullary cords, and sinuses (). They are both structural and functional compartments serving as sites of immunologic reactions for specific antigenic stimuli.Figure 36-2

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FIGURE 36-2 Diagram of a normal lymph node showing cortical, paracortical, and medullary compartments.

Cortex

The lymph node is surrounded by a capsule of fibrous tissue. Immediately below the capsule is the cortex, the most superficial portion of the lymph node consisting of primary and secondary follicles. Primary follicles are microscopic aggregates of small naive B lymphocytes. These lymphocytes express pan-B cell markers, including CD19 and CD20 and are frequently CD5+ (Figure 36-3). The formation of secondary follicles with germinal centers and their functions are assisted by follicular dendritic cell meshworks, best visualized by immunohistochemical stains such as CD21.23 On antigen encounter, naive B lymphocytes undergo transformation, proliferation, and differentiation into precursors of antibody-producing plasma cells and memory B cells (Figure 36-3). The remaining naive B cells are displaced into the periphery of the germinal center and form the mantle zone.

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FIGURE 36-3 Differentiation stages of mature B cells. Note changes in immunophenotype at specific stages of differentiation. BCL, B cell lymphoma; sIg, surface immunoglobin.

Germinal center B cells have a specific immunophenotype. In addition to pan-B cell markers, they express germinal center cell antigens CD10 and BCL6, and, in contrast to circulating B cells, they lack anti-apoptotic BCL2 protein. Functional compartments of the germinal center include the dark zone occupied by centroblasts, large B cells with round vesicular nuclei, small nucleoli adjacent to nuclear membrane, and basophilic cytoplasm (). The dark zone is a site of high proliferative activity and somatic mutations of B cell immunoglobulin variable regions. The latter process allows for the production of immunoglobulins with the best affinity for a particular antigen. Figure 36-4

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FIGURE 36-4 Secondary follicle with well-developed polarization in germinal center showing dark zone (DZ) and light zone (LZ). Note the presence of numerous tingible body macrophages (arrows). A distinct mantle zone (MZ) also is present at the periphery of the germinal center (hematoxylin and eosin stain, ×100).

After completing somatic mutations, centroblasts differentiate into centrocytes, smaller cells with dense chromatin and irregular nuclear outlines, which form the light zone (Figure 36-4). Subsequently, centrocytes with low-affinity (“unfit”) surface immunoglobulins undergo apoptosis and are phagocytized by germinal center macrophages (tingible-body macrophages). The presence of numerous macrophages with apoptotic debris contributes to the characteristic “starry sky” pattern of the germinal center. Centrocytes with immunoglobulins with high affinity for a particular antigen lose their germinal center antigens (CD10 and BCL6) and differentiate into memory B cells that form a marginal zone at the periphery of the mantle zone. Marginal zone lymphocytes are medium sized with abundant clear cytoplasm and indented nuclei.

In the final step of B cell differentiation are plasma cells that reside in medullary cords of lymph nodes and that also migrate to bone marrow. Plasma cells are negative for pan-B cell antigens and surface immunoglobulins; however, they express CD138, CD38, and cytoplasmic immunoglobulins.

Paracortex

The paracortex occupies the area separating the follicles and extends toward medullary cords. This compartment generates immunocompetent T cells and is occupied predominantly by T cells, interdigitating dendritic cells (antigen-presenting cells), and high-endothelial venules. The last are specialized vessels serving as a gate of entry for lymphocytes from peripheral blood into lymph nodes. T cells express pan-T cell antigens such as CD3, CD5, CD2, and CD7. Both CD4+ and CD8+ T lymphocytes are seen in paracortex. Similar to B cells, T cells transform in response to antigen stimulation. In this process, small lymphocytes become immunoblasts: large lymphoid cells with vesicular nuclei; prominent, often single, nucleoli; and abundant basophilic cytoplasm. The paracortex also contains numerous B immunoblasts.

Medulla

The medulla represents the innermost portion of the lymph node surrounding the hilum. This area is composed of medullary cords with plasma cells and medullary sinuses.

Sinuses

The filtration of lymphatic fluid through lymph nodes is accomplished via afferent lymphatics communicating with a subcapsular sinus, which is situated immediately beneath the capsule (Figure 36-2). The subcapsular sinus drains into cortical sinuses, which run through the cortex and empty to medullary sinuses. The latter converge into the efferent lymphatic vessel at the hilum. The sinuses are filled with macrophages or sinus histiocytes. These cells play an important role in antigen capture and processing.

Lymph node processing

Current approach to diagnosis of lymphomas incorporates routine light microscopic examination and ancillary techniques. During processing of excised lymph nodes, appropriate steps should be taken to ensure adequate preservation of the tissue and its availability for all necessary studies. The appropriate transport conditions need to be maintained to preserve tissue integrity and prevent drying. Immediately after excision, the lymph node should be transported to the pathology laboratory in a sealed sterile jar on gauze pads moistened with sterile saline or in tissue culture media. The fresh lymph node is cut into 3-mm-thick sections for the evaluation of nodal architecture. If areas of granulomas or suppuration are present, a portion of the tissue should be sent for cultures.

Touch imprints can be prepared to ensure the adequacy of the specimen and to perform special studies. To obtain an adequate imprint, a freshly cut tissue surface is gently touched to the glass slide and pulled away. Touch imprints can be fixed in formalin or alcohol solution or air-dried for subsequent Wright-Giemsa staining. Storing of fixed touch imprints for immunocytochemical studies is optional because currently immunophenotyping is most commonly performed on paraffin-embedded tissue or using flow cytometry. The latter is particularly helpful in confirming monoclonal light chain expression.

Several thin lymph node sections are placed in 10% buffered formalin for paraffin embedding. Some pathology laboratories fix additional tissue samples in a variety of fixatives with protein-precipitating properties (B5 fixative, zinc chloride formalin) for better preservation of cytologic detail.4 Regardless of fixative used, thin sectioning of a fresh lymph node is crucial for proper tissue permeation and fixation. A portion of lymph node is placed in culture medium (Roswell Park Memorial Institute medium) and transported to a flow cytometry laboratory for immunophenotyping. The remaining fresh tissue can be stored at –70° C for further studies.

Reactive lymphadenopathies

Lymphadenopathy, lymph node enlargement, can occur in benign/reactive and malignant conditions. Reactive lymphadenopathies can affect any compartment of a lymph node and present as expansion of normal nodal structures. Reactive hyperplasias are classified into several patterns, as follows:

1. Follicular

2. Paracortical

3. Sinusoidal

4. Mixed

Follicular pattern

Follicular hyperplasia is the most common form of reactive lymphadenopathies. It is frequently seen in lymph nodes and tonsils of children and adolescents as a reaction to infections. In adults, it occurs in association with infections, autoimmune disorders (rheumatoid arthritis, systemic lupus erythematosus), syphilis, and early human immunodeficiency virus (HIV) infection. Microscopically, an expansion of reactive follicles can be prominent and extend beyond the cortex into the medulla (). Secondary follicles retain all the hallmarks of reactive germinal centers, including distinct polarization, presence of tingible-body macrophages, abundant mitotic figures, and preserved mantle zones (Figure 36-5Figure 36-4).

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FIGURE 36-5 Reactive follicular hyperplasia with numerous secondary follicles scattered throughout the lymph node (hematoxylin and eosin stain, ×40).

Paracortical pattern

Paracortical expansion is associated with viral infections (e.g., infectious mononucleosis) and drug reactions and is also seen in patients with chronic skin diseases (dermatopathic lymphadenopathy). In addition to small lymphocytes, the paracortex shows numerous immunoblasts, increased mitotic activity, and vascular proliferation (). Focal areas of necrosis may also be seen. In dermatopathic lymphadenopathy, the paracortex has a characteristic mottled appearance as a result of an increased number of large cells with abundant clear cytoplasm scattered among small lymphoid cells (Figure 36-6Figure 36-7). These cells include histiocytes, often carrying melanin pigment, and Langerhans cells (Figure 36-8). Scattered immunoblasts, plasma cells, eosinophils, and vascular proliferation are also encountered.

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FIGURE 36-6 Immunoblasts (arrows) scattered in the paracortex (hematoxylin and eosin stain, ×1000).

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FIGURE 36-7 Paracortical hyperplasia. Note mottled appearance of the paracortex resulting from multiple scattered histiocytes with abundant cytoplasm (arrows) (hematoxylin and eosin stain, ×40).

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FIGURE 36-8 Dermatopathic lymphadenopathy in a patient with chronic skin rash. Scattered pigment-laden macrophages (arrow) are present in the paracortical area (hematoxylin and eosin stain, ×400).

Sinusoidal pattern

Expanded subcapsular, cortical, and medullary sinuses are often seen in lymph nodes draining limbs, abdominal organs, various inflammatory lesions, and malignancies. In select cases, the prominent sinuses compress the nodal parenchyma. They may be completely filled with histiocytes showing abundant cytoplasm, a small oval nucleus with inconspicuous nucleolus, and delicate chromatin. Monocytoid B cells with abundant cytoplasm and oval indented nuclei that may mimic histiocytes are seen in HIV-associated lymphadenopathy and Toxoplasma lymphadenitis (Figure 36-9A). Numerous malignant lesions show predilection for sinuses, such as Langerhans cell histiocytosis, B and T cell lymphomas, and carcinomas; therefore, a thorough evaluation of expanded sinuses under high magnification is always necessary.

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FIGURE 36-9 Toxoplasma lymphadenitis. A, Monocytoid B cells are medium sized with irregular nuclear outlines and abundant cytoplasm (shown in center circle) (hematoxylin and eosin stain, ×400). B, Classic triad of reactive changes seen in Toxoplasma lymphadenitis includes follicular hyperplasia with focal aggregates of histiocytes (H) and monocytoid B cells (MBC). An irregular outline of a secondary follicle is seen on the left (arrowheads) (hematoxylin and eosin stain, ×100).

Mixed pattern

A classic example of mixed-pattern hyperplasia is seen in Toxoplasma gondii infection, a common protozoal infection typically seen after ingestion of raw meat or contamination by cat feces. The expansion of all lymph node compartments is seen (Figure 36-9). Florid follicular hyperplasia is accompanied by paracortical expansion, aggregates of histiocytes encroaching on germinal centers, and expanded sinuses. Sinuses are focally filled with a specific subset of B cells, so-called monocytoid B cells.

Lymphomas

Approximately 86,000 new cases of lymphoma are diagnosed annually in the United States.5 Most lymphomas develop in previously healthy individuals. The strongest risk factor for development of lymphoproliferative disorder is altered immune function as seen in immunocompromised patients or individuals with autoimmune diseases.67 Similarly, certain viral and bacterial infections are associated with a higher risk for the development of lymphoma.8 Accumulating evidence indicates that exposure to chemicals and herbicides may predispose to lymphoid neoplasms. Most lymphomas present in lymph nodes. Certain types show a predilection for extranodal sites. The frequency of bone marrow and peripheral blood (leukemic phase) involvement varies, depending on the lymphoma subtype.

Over the years, numerous classification systems have been proposed based mainly on the morphology and clinical characteristics (e.g., Rappaport classification, Kiel classification, Working Formulation). With increased understanding of the development and function of the immune system, however, it became clear that lymphomas, like myeloid neoplasms, recapitulate normal stages of lymphoid differentiation. In addition, the elucidation of specific molecular events occurring in lymphomagenesis helped in devising clinically relevant classification, especially for morphologically heterogeneous entities. Currently, numerous types of lymphoma are distinguished based on morphology, immunophenotype, molecular genetics, and clinical and laboratory characteristics. The integration of these features is mandatory for comprehensive lymphoma diagnosis. On the basis of cellular origin, lymphomas can be categorized into lesions of lymphoid precursors and neoplasms of mature lymphoid cells (). Table 36-1 In this chapter, only mature B cell and T cell neoplasms are discussed; the precursor malignancies are covered in Chapter 35.

TABLE 36-1

2008 World Health Organization Classification of Mature Lymphoid Neoplasms

Type of Lymphoma

Examples

Mature B cell lymphomas

Chronic lymphocytic leukemia/small lymphocytic lymphoma 

B cell prolymphocytic leukemia 

Splenic B cell marginal zone lymphoma 

Hairy cell leukemia 

Splenic B cell lymphoma/leukemia, unclassifiable 

Splenic diffuse red pulp small B cell lymphoma 

Hairy cell leukemia-variant 

Lymphoplasmacytic lymphoma 

Heavy chain diseases 

Gamma heavy chain disease 

Mu heavy chain disease 

Alpha heavy chain disease 

Plasma cell neoplasms 

Monoclonal gammopathy of undetermined significance (MGUS) 

Plasma cell myeloma 

Solitary plasmacytoma of bone 

Extraosseous plasmacytoma 

Monoclonal immunoglobulin deposition diseases 

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) 

Nodal marginal zone lymphoma 

Follicular lymphoma 

Primary cutaneous follicle center lymphoma 

Mantle cell lymphoma 

Diffuse large B cell lymphoma (DLBCL), not otherwise specified 

T cell/histiocyte-rich large B cell lymphoma 

Primary DLBCL of the central nervous system 

Primary cutaneous DLBCL, leg type 

Epstein-Barr virus (EBV)–positive DLBCL of the elderly 

DLBCL associated with chronic inflammation 

Lymphomatoid granulomatosis 

Primary mediastinal (thymic) large B cell lymphoma

 

Intravascular large B cell lymphoma 

ALK-positive large B cell lymphoma 

Plasmablastic lymphoma 

Large B cell lymphoma arising in human herpesvirus 8–associated multicentric Castleman disease 

Primary effusion lymphoma 

Burkitt lymphoma 

B cell lymphoma, unclassifiable, with features intermediate between those of DLBCL and Burkitt lymphoma 

B cell lymphoma, unclassifiable, with features intermediate between those of DLBCL and classical Hodgkin lymphoma

Mature T cell lymphomas

T cell prolymphocytic leukemia 

T cell large granular lymphocytic leukemia 

Chronic lymphoproliferative disorder of natural killer (NK) cells 

Aggressive NK cell leukemia 

EBV-positive T cell lymphoproliferative diseases of childhood 

Systemic EBV-positive T cell lymphoproliferative diseases of childhood 

Hydroa vacciniforme–like lymphoma 

Adult T cell leukemia/lymphoma 

Extranodal NK/T cell lymphoma, nasal type 

Enteropathy-associated T cell lymphoma 

Hepatosplenic T cell lymphoma 

Subcutaneous panniculitis-like T cell lymphoma 

Mycosis fungoides 

Sézary syndrome 

Primary cutaneous CD30+ T cell lymphoproliferative disorders 

Primary cutaneous peripheral T cell lymphomas, rare subtypes 

Primary cutaneous gamma-delta T cell lymphoma 

Primary cutaneous CD8+ aggressive epidermotropic cytotoxic T cell lymphoma 

Primary cutaneous CD4+ small/medium T cell lymphoma 

Peripheral T cell lymphoma, not otherwise specified 

Angioimmunoblastic T cell lymphoma 

Anaplastic large cell lymphoma, ALK positive 

Anaplastic large cell lymphoma, ALK negative

Mature B cell lymphomas

Mature B cell lymphomas are derived from various stages of B cell differentiation. Although they show significant morphologic and immunophenotypic heterogeneity, all B cell lymphomas produce monoclonal light chain immunoglobulins, clonal immunoglobulin gene rearrangements, or both. Follicular lymphoma and diffuse large B cell lymphoma (DLBCL) are the most common subtypes of B cell lymphoma.9 Most cases are lymph node based and occur in elderly individuals. However, leukemic involvement (peripheral blood and bone marrow) can occur with any lymphoma type. The most common mature B cell neoplasms are discussed in the following paragraphs and are summarized in Table 36-2.

TABLE 36-2

Morphologic and Immunophenotypic Features of Mature B-Cell Lymphomas

Subtype

Architectural Features

Cytologic Characteristics

Immunophenotype/Cytogenetics

Cell of Origin

Chronic lymphocytic leukemia/small lymphocytic lymphoma

Diffuse lymphocytic proliferation with growth centers

Small lymphoid cells

CD20+, CD19+, CD5+, CD23+, LEF1

Memory and marginal zone B cells

B cell prolymphocytic leukemia

Diffuse proliferation

Medium-sized lymphoid cells with distinct “punched-out” nucleoli and abundant cytoplasm

CD20+, CD19+, FMC7+, CD5+/

Unknown mature B cell

Mantle cell lymphoma

Diffuse, nodular, or mantle zone pattern

Medium-sized lymphocytes with irregular nuclei

CD20+, CD19+, CD5+, FMC7+, SOX11, cyclin D1+, t(11; 14)

Mantle zone cell

Follicular lymphoma

Follicular pattern

Medium-sized lymphocytes with indented nuclei and variable numbers of large lymphoid cells



CD20+, CD19+, CD10+, BCL6+, BCL2+, t(14; 18)

Germinal center cell

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue

Diffuse lymphoid proliferation, occasionally marginal zone or nodular pattern

Medium-sized lymphocytes with irregular nuclei and clear abundant cytoplasm

CD20+, CD19+, CD43+/

Marginal zone cell

Plasma cell myeloma, plasmacytoma

Sheets or large aggregates of plasma cells

Plasma cells, frequently with cytologic atypia

CD20, CD19+/, CD38+, CD138+, cytoplasmic light chain+

Plasma cell

Diffuse large B cell lymphoma

Diffuse proliferation

Large lymphoid cells

CD20+, CD19+, CD10+/, BCL6+/, BCL2+/, CD5+/

Different stages of mature B cells

Burkitt lymphoma

Diffuse lymphoid proliferation with “starry sky” pattern

Medium-sized lymphocytes with evenly distributed chromatin, inconspicuous nucleoli

CD20+, CD19+, CD10+, BCL6+, BCL2, high proliferative activity, t(8:14)

Germinal center cell

Chronic lymphocytic leukemia/small lymphocytic lymphoma

Definition. 

Chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) are characterized by accumulation of small lymphoid cells in peripheral blood, bone marrow, and lymphoid organs. The exact cell of origin in CLL/SLL is not known, however gene expression profiling has shown that antigen-experienced B cells, both memory B cells and marginal zone B cells, are likely candidates.10 The World Health Organization (WHO) classification scheme considers CLL and SLL as one entity with different clinical presentations.1 The diagnosis of CLL/SLL is based on the predominant site of involvement. CLL presents mostly in peripheral blood and bone marrow. SLL primarily involves lymph nodes and other lymphoid organs.

Morphology. 

In CLL, bone marrow and peripheral blood films show small lymphoid cells with a characteristically coarse chromatin (“soccer-ball” pattern), absent or inconspicuous nucleoli, and scant cytoplasm111 (Figure 36-10). According to the 2008 International Workshop on Chronic Lymphocytic Leukemia, up to 55% of the cells in CLL may include prolymphocytes (larger lymphoid cells with pale blue cytoplasm, less condensed chromatin, and a distinct nucleolus), lymphoid cells with cleaved nuclei, or large lymphoid cells with an atypical appearance.12 The French-American-British (FAB) Cooperative Group has proposed, and other groups have supported, a morphologic classification of CLL consisting of two major types: typical CLL (> 90% small mature lymphocytes and < 10% prolymphocytes) and an atypical CLL category.13141516 The 2008 WHO classification of lymphoid malignancies does not divide CLL into typical and atypical types.1

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FIGURE 36-10 Chronic lymphocytic leukemia/small lymphocytic lymphoma. Peripheral blood film showing small lymphocytes and smudge cells (arrows) (Wright-Giemsa stain, ×1000).

Smudge cells, representing disintegrated lymphoid cells, are typically seen on peripheral blood films of CLL patients. Smudge cells are helpful in the diagnosis because they are not often seen in other subtypes of malignant lymphoma. The bone marrow biopsy specimen shows nodular, diffuse, or interstitial infiltrates of small lymphoid cells (). Figure 36-11

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FIGURE 36-11 Chronic lymphocytic leukemia/small lymphocytic lymphoma. Bone marrow biopsy specimen with nodular (right) and interstitial lymphoid infiltrate composed of small lymphocytes (hematoxylin and eosin stain, ×400).

Lymph nodes involved by SLL show an effacement of normal nodal architecture by a diffuse proliferation of small, round lymphoid cells with coarse chromatin, indistinct nucleoli, and scant cytoplasm (, Figure 36-12 A). In addition, scattered nodules (so-called pseudofollicles, growth centers, or proliferation centers) composed of medium-sized and large lymphoid cells with dispersed chromatin and distinct nucleoli are observed (Figure 36-12B). The diffuse proliferation of small lymphoid cells with pseudofollicles is pathognomonic for SLL.

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FIGURE 36-12 Chronic lymphocytic leukemia/small lymphocytic lymphoma in a lymph node. A, Diffuse proliferation of small lymphoid cells (hematoxylin and eosin stain, ×100). B,Proliferation center with large and medium-sized lymphoid cells in a background of small lymphocytes (hematoxylin and eosin stain, ×400).

Diagnosis and immunophenotype. 

CLL is diagnosed based on a sustained increase in the monoclonal B lymphocytes with CLL immunophenotype which is equal or greater than 5000/uL. The CLL immunophenotype includes an expression of CD19, CD20, and CD23, with aberrant expression of CD5.1 Expression of CD20 and CD79b is weaker than in normal B cells.1 Immunophenotyping also demonstrates expression of kappa or lambda light chains (clonal light chain restriction).112

CD23 and LEF1 (lymphoid-enhancer-binding factor 1) expression and the absence of FMC7, cyclin D1, and SOX11 distinguish CLL/SLL from mantle cell lymphoma. The presence of less than 5000/μL of circulating monoclonal B cells with a CLL/SLL immunophenotype can be found in a small proportion of healthy individuals and has been designated a monoclonal B-cell lymphocytosis.117 Therefore, the demonstration of these cells by flow cytometry must always be interpreted in the context of other clinical and laboratory features.17

Clinical features and prognosis. 

CLL/SLL generally affects older adults, however approximately 24% of patients are less than 55 years old.18 In CLL most patients are asymptomatic at diagnosis. The first indication of disease is often an incidental finding of lymphocytosis on a routine CBC in a blood count ordered for a different reason.

CLL is a heterogeneous disease in terms of clinical behavior. A variety of features have been used over the years to predict patient outcomes, including staging systems based on the extent of lymphoid organ involvement and degree of cytopenias. More recently, a growing number of biologic and molecular markers are being used which have enabled a more accurate assessment of disease status and prognosis.

The somatic mutation status of the variable region of the immunoglobulin heavy chain (IGVH) locus has divided the disease into two groups with considerably different outcomes.11 Approximately 55% of CLL patients have mutated IGVH, indolent disease, and a median survival time of 24 years.1920 On the other hand, patients with unmutated IGVH have aggressive disease and a median survival of approximately 8 years.1920 At diagnosis, patients can be routinely screened using techniques such as fluorescent in situ hybridization (FISH) for the presence of chromosomal abnormalities, del13q14.3, del11q22-23, trisomy 12, and del17p13, which provide information regarding predicted survival (good, poor, intermediate, and very poor, respectively).20 Next generation sequencing has recently identified additional significant genetic mutations such as EZH2, NOTCH1SF3B1, and BIRC3, which can be used for an assessment of prognosis.21 The timing as well as selection of the most appropriate treatment approach has also been the subject of intense research. Independent of the course of the original disease, approximately 5% of patients with CLL/SLL develop a high-grade diffuse large B cell lymphoma (called Richter syndrome) with a survival of less than 1 year.16

Prolymphocytic leukemia

Definition. 

Prolymphocytic leukemia (PLL) is a rare mature lymphoid leukemia that can be derived from B or T cells. Both B cell and T cell types involve peripheral blood, bone marrow, and spleen. Lymph node involvement is more commonly seen in T cell PLL. This lymphoproliferative disease is distinct from CLL, and its diagnosis requires that more than 55% of circulating lymphoid cells have the morphology of a prolymphocyte.

Morphology and immunophenotype. 

The pathognomonic cell of B cell PLL is a prolymphocyte of medium size with round nucleus, moderately abundant cytoplasm, and distinct “punched-out” nucleolus (). The cell size (twice that of a normal lymphocyte) and prominent central nucleolus allow PLL to be distinguished from CLL/SLL. The peripheral blood involvement in PLL is prominent, with a white blood cell count frequently in excess of 100 × 10Figure 36-139/L. Bone marrow shows interstitial and/or nodular proliferation of prolymphocytes. Both white and red splenic pulp are infiltrated by PLL. B cell PLL is positive for pan–B cell markers CD20, CD19, CD22, and FMC7. The density of CD20 and surface light chain is higher than in typical cases of CLL/SLL. A proportion of cases are positive for CD5 antigen. In such cases, distinguishing the PLL from mantle cell lymphoma presenting with a leukemic involvement might be challenging and requires cytogenetic or molecular studies to exclude the presence of t(11; 14) (refer to the section on mantle cell lymphoma).

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FIGURE 36-13 Peripheral blood film showing a characteristic morphology of prolymphocytes (medium size, abundant cytoplasm, distinct nucleoli) (×1000).

Morphologic features of T cell PLL are not as distinct as those of the B cell type. Neoplastic cells seen in peripheral blood films are small to medium size, with round or irregular nuclei, the latter resembling Sézary cells. Prominent nucleoli are seen only in a proportion of cases. Cytoplasmic blebbing is common. Bone marrow, spleen, lymph node, and occasionally skin involvement is diffuse, with accentuation in nodal paracortical areas and around the vessels in dermis. The diagnosis of T cell PLL is challenging when attempted using morphologic features alone. A combination of morphologic, clinical, and immunophenotypic features is most helpful in making the diagnosis. T prolymphocytes are positive for T cell markers such as CD3, CD2, and CD5. In contrast to many T cell lymphomas, T cell PLL is positive for CD7 antigen. Most commonly CD4 antigen is expressed. A minority of cases can be double positive for CD4 and CD8, or positive for CD8.

Clinical features and prognosis. 

Like CLL/SLL, PLL is a disease of the elderly (mean age of presentation is 70 years). Overall prognosis is poor (median survival is 3 years for B cell PLL), partly due to the high incidence of mutation in the tumor suppressor gene TP53 and the unavailability of targeted therapy.22 T cell PLL is an aggressive disease with a median survival of 1 year when conventional chemotherapies are used. Recently, addition of monoclonal antibody therapy against CD52 (alemtuzumab) has significantly improved treatment response and survival of patients with T cell PLL.

Hairy cell leukemia

Definition. 

Hairy cell leukemia is characterized by small B lymphocytes with abundant cytoplasm and fine (“hairy”) cytoplasmic projections. The postulated cell of origin is the peripheral B cell of post–germinal center stage (memory B cell).

Morphology and immunophenotype. 

Hairy cell leukemia cells are found predominantly in bone marrow and the red pulp of the spleen. A low number of neoplastic B cells are seen in peripheral blood. Lymph node involvement is rare. The bone marrow infiltrates are interstitial and are composed of small to medium-sized lymphoid cells with abundant cytoplasm (, Figure 36-14 A). The bone marrow involvement may be subtle with preservation of normal hematopoiesis. As a result of the production of fibrogenic cytokines by leukemic cells, a bone marrow biopsy specimen shows an increase in reticulin fibers. The characteristic cytologic features of neoplastic cells are best appreciated in bone marrow aspirate and peripheral blood films. Neoplastic cells display an oval or indented nucleus, abundant cytoplasm, and fine, hairlike cytoplasmic projections (Figure 36-14B).

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FIGURE 36-14 Hairy cell leukemia. A, Interstitial bone marrow infiltrate composed of widely spaced lymphoid cells with abundant cytoplasm and irregular nuclei (hematoxylin and eosin stain, ×1000). B, Lymphoid cells of hairy cell leukemia show characteristic cytoplasmic projections, which are supported by the peripheral cytoplasmic network of polymerized actin (peripheral blood, Wright-Giemsa stain, ×1000).

Typical cases of hairy cell leukemia show strong positivity for B cell markers (CD19, CD20, CD22) coupled with bright expression of CD11c, CD25, CD103, tartrate-resistant acid phosphatase (TRAP, demonstrated by immunohistochemical analysis or cytochemical stain), DBA-44, CD123, and annexin A1. CD123 and annexin A1 are the most specific markers for classic hairy cell leukemia and can help in differentiating hairy cell leukemia from splenic marginal zone lymphoma. These antibodies, available for both flow cytometry and paraffin-embedded tissues, replaced the TRAP cytochemical stain previously commonly used to establish the diagnosis of hairy cell leukemia.

Clinical features and prognosis. 

Hairy cell leukemia is a rare lymphoproliferative disorder occurring in middle-aged individuals (median age, 55 years). The presenting signs include splenomegaly and pancytopenia. Durable remissions can be achieved using purine analogues. Conventional lymphoma therapy is not effective.

Mantle cell lymphoma

Definition. 

Mantle cell lymphoma is a lymphoproliferative disorder characterized by medium-sized lymphoid cells with irregular nuclear outlines derived from the follicular mantle zone.23

Morphology and immunophenotype. 

The main sites of presentation are lymph nodes. Bone marrow, peripheral blood, spleen, and gastrointestinal tract also are frequently involved. Most commonly, lymph nodes show a replacement of normal nodal architecture with a diffuse proliferation of monotonous, medium-sized lymphoid cells with irregular nuclear outlines (Figure 36-15A). Occasionally, lymph nodes demonstrate a vaguely nodular pattern or partial preservation of nodal architecture with a prominent thickening of mantle zones (Figure 36-15B). Peripheral blood involvement by mantle cell lymphoma can mimic PLL (Figure 36-15C).

Image 

FIGURE 36-15 Mantle cell lymphoma. A, Diffuse proliferation of medium-sized lymphoid cells with irregular nuclei (hematoxylin and eosin stain, ×1000). B, Mantle zone pattern. Regressed germinal center is seen in the center (hematoxylin and eosin stain, ×100). C, Circulating mantle cell lymphoma cells with a few showing indented nuclei reminiscent of the cleaved nuclei seen in histologic sections (peripheral blood film, Wright-Giemsa stain, ×1000).

Like other B cell lymphoproliferative disorders, mantle cell lymphoma shows expression of pan–B cell markers (CD19, CD20) and high-density clonal surface light chains. There is coexpression of CD5 antigen; however, CD23 antigen is absent. In contrast to CLL/SLL, the expression of CD20 and light chains is strong, and there is immunoreactivity for cyclin D1 and SOX11. Cyclin D1 (BCL1) is a proto-oncogene involved in the regulation of G1 to S phase transition. In mantle cell lymphoma, this gene is constitutively expressed through its translocation to the immunoglobulin heavy chain gene, t(11; 14). This cytogenetic abnormality is present in the majority of mantle cell lymphomas. Cyclin D1-negative cases are positive for SOX11, a recently described diagnostic and prognostic marker present in the majority of cases of mantle cell lymphoma.

Clinical features and prognosis. 

Mantle cell lymphoma is an aggressive lymphoproliferative disorder with a median survival time of 3 to 5 years. Most patients present with disseminated disease, including bone marrow involvement. This lymphoma is incurable with currently available chemotherapy, but stem cell transplantation is successful in a proportion of patients.

Follicular lymphoma

Definition. 

Follicular lymphoma originates from germinal center B cells and in most cases recapitulates follicular architecture.

Morphology and immunophenotype. 

Numerous closely spaced follicles replace the normal nodal architecture (). The neoplastic proliferation may extend into perinodal adipose tissue. In contrast to the reactive secondary follicles, in follicular lymphoma the mantle zone and polarization are absent. The neoplastic follicles are composed of medium-sized lymphoid cells with angular or indented nuclei, cytologically similar to centrocytes, with a variable admixture of large lymphoid cells. The latter resemble centroblasts and show oval nuclei with vesicular chromatin and several nucleoli located close to nuclear membrane. The relative proportion of medium-sized and large lymphoid cells is of prognostic significance. Cases with high numbers of large cells show a more aggressive clinical course, similar to that of DLBCL. Therefore, follicular lymphomas are graded by counting the average number of large cells per high-power field.Figure 36-161 Two grades are recognized: grade 1-2 shows rare scattered large lymphocytes, and grade 3 follicular lymphomas are composed of numerous centroblasts.

Image 

FIGURE 36-16 Follicular lymphoma. Nodular proliferation replacing normal elements of lymph node architecture (hematoxylin and eosin stain, ×40).

The immunophenotype reflects the follicle center cell origin of this disease. Pan–B cell markers (CD19, CD20) are present, along with the coexpression of CD10, BCL6, and clonal surface immunoglobulin. In contrast to reactive follicles, neoplastic cells express BCL2 protein. This protein is responsible for the decreased sensitivity of lymphoma cells to apoptosis and allows the accumulation of neoplastic lymphocytes. The expression of BCL-2 by follicular lymphoma cells is due to the t(14; 18)(q32; q21), which places the BCL2 gene under a promoter of the immunoglobulin heavy chain gene. This cytogenetic abnormality is present in 95% of cases.24

Clinical features and prognosis. 

The median age at diagnosis is 59 years. Most patients present with disseminated disease. Bone marrow involvement is present in approximately 50% of cases. The course of the disease is indolent in grade 1-2 follicular lymphoma, whereas grade 3 cases are more aggressive and are treated in a manner similar to DLBCL with doxorubicin (Adriamycin)–based regimens.

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue

Definition. 

Three subtypes of marginal zone lymphomas are recognized: nodal, extranodal (MALT lymphoma), and splenic. In this chapter, we focus on the extranodal variant derived from marginal zone cells of MALT. In this lymphoma, the neoplastic proliferation is usually heterogeneous, encompassing small and medium-sized lymphocytes, plasma cells, and scattered large lymphoid cells. MALT lymphoma is frequently associated with autoimmune conditions (e.g., Sjögren syndrome, Hashimoto thyroiditis) or infections (Helicobacter pylori gastritis or hepatitis C).25 Persistent immune stimulation leads to the accumulation of reactive lymphoid tissue and subsequently to the development of marginal zone lymphoma. The importance of continuous antigenic stimulation in the early stages of these lymphomas is shown by the remission of the disease, when associated infection is eradicated with antibiotic therapy.26

Morphology and immunophenotype. 

In most cases, the neoplastic population is composed of a mixture of medium-sized lymphocytes, plasma cells, and occasional large lymphoid cells. There is a predominance of medium-sized marginal zone cells with irregular nuclei (, Figure 36-17 A). Residual reactive germinal centers may be present, which are colonized to variable degrees by neoplastic cells. A characteristic feature of MALT lymphoma is the presence of so-called lymphoepithelial lesions, representing the invasion of the neoplastic lymphocytes into the glandular epithelium (Figure 36-17B). This feature is usually absent from reactive lymphoid proliferations associated with autoimmune processes or infections.

Image 

FIGURE 36-17 Mucosa-associated lymphoid tissue lymphoma. A, Heterogeneous population of medium-sized lymphoid cells with abundant clear cytoplasm and occasional large cells (hematoxylin and eosin stain, ×500). B, Lymphoepithelial lesion. Malignant lymphocytes invading glandular epithelium (hematoxylin and eosin stain, ×1000).

The neoplastic cells of marginal zone lymphoma express CD20, CD19, and monoclonal immunoglobulin chains. CD5 and CD10 are absent. CD43 antigen is coexpressed in 30% of cases and can be a helpful feature in diagnosing marginal zone lymphoma when there is a significant residual reactive component. In select cases, the demonstration of clonality by flow cytometry or by polymerase chain reaction (PCR) analysis of immunoglobulin heavy chain (IgH) gene rearrangements may be necessary to confirm the diagnosis.

Antigenic stimulation and interference with the apoptotic pathway play an important role in the pathogenesis of MALT lymphoma. Approximately 30% of cases show a translocation involving apoptosis-inhibitor gene API2 and the MLT gene, the t(11; 18)(q21; q21).27

Clinical features and prognosis. 

The gastrointestinal tract is the most common site for extranodal marginal zone lymphoma. The lung, thyroid, ocular adnexa, and breast are other primary sites of involvement. In most cases, the disease is localized to a primary site and regional lymph nodes. Bone marrow is less frequently involved than in other types of indolent lymphoma.28 In cases of gastric MALT lymphoma positive for H. pylori, the antibiotic treatment of the infection may induce a remission of the associated lymphoma. Other cases may benefit from local therapy.

Plasma cell neoplasms

Definition. 

Plasma cell neoplasms are characterized by a monoclonal proliferation of terminally differentiated B cells (i.e., plasma cells). These disorders can present as a localized or disseminated process most commonly involving bone marrow and bone. The clinical features and the primary site of involvement define distinct clinicopathologic entities (). Table 36-3

TABLE 36-3

Clinicopathologic Features of Selected Plasma Cell Neoplasms

Plasma Cell Disorder

Defining Features

Plasma cell myeloma

Monoclonal protein in serum or urine 

Clonal plasma cells in bone marrow or presence of plasmacytoma 

Organ or tissue impairment (CRAB: hypercalcemia, renal insufficiency, anemia, bone lesions)

Plasma cell leukemia

Clonal plasma cell population in bone marrow and other features of plasma cell myeloma in conjunction with peripheral blood involvement: > 2 × 109/L or > 20% circulating plasma cells 

May present with involvement of spleen, liver, and body cavity fluid including cerebrospinal fluid

Monoclonal gammopathy of undetermined significance

Bone marrow plasmacytosis (< 10% plasma cells) 

Monoclonal gammopathy (< 30 g/L) 

No lytic bone lesions or organ/tissue impairment

Solitary plasmacytoma of bone

Localized bone mass composed of plasma cells

Extraosseous plasmacytoma

Localized extraosseous mass composed of plasma cells

Plasma cell myeloma is a multifocal accumulation of malignant plasma cells in bone marrow presenting as lytic bone lesions. In most cases, monoclonal immunoglobulin produced by neoplastic plasma cells is detected in serum, urine, or both (monoclonal gammopathy). The overt disease may be preceded by an asymptomatic period of monoclonal gammopathy with only mild bone marrow plasmacytosis (fewer than 10% plasma cells). Approximately 25% of asymptomatic patients with clonal serum immunoglobulin progress to symptomatic plasma cell myeloma.29 The term monoclonal gammopathy of undetermined significance(MGUS) is used to encompass the entire patient population with clonal serum immunoglobulin and only mild marrow plasmacytosis. Plasmacytoma, a localized form of plasma cell neoplasm, may present as a solitary bone lesion or involve an extraosseous or extramedullary site, most commonly the nasopharynx, oropharynx, or sinuses.

Morphology and immunophenotype. 

Plasma cell myeloma is characterized by marked bone marrow plasmacytosis. Large aggregates and sheets of plasma cells, frequently with cytologic atypia, are present and often constitute more than 30% of marrow cellularity (, Figure 36-18 A). Atypical cytologic features seen in plasma cell myeloma include a high nuclear-to-cytoplasmic ratio, dispersed chromatin pattern, and distinct nucleoli (Figure 36-18B). These changes are rarely seen in reactive conditions and MGUS. Similarly, in reactive plasmacytosis associated with infections and autoimmune disorders, plasma cells appear scattered throughout the marrow and form small clusters around the vessels. Large aggregates and sheets of plasma cells, which are commonly seen in plasma cell myeloma, are not present in reactive conditions. Rarely, patients with plasma cell myeloma show a marked increase in circulating plasma cells. The term plasma cell leukemia is reserved for cases with more than 20% circulating plasma cells or plasma cell counts exceeding 2 × 109/L. Neoplastic plasma cells can also infiltrate spleen, liver, or lymph nodes and involve body cavity fluids (Figure 36-18C). Plasmacytoma represents a localized, mass-forming, monoclonal plasma cell proliferation.

Image 

FIGURE 36-18 Plasma cell myeloma. A, Bone marrow biopsy specimen showing large aggregates of plasma cells (hematoxylin and eosin stain, ×400). B, Neoplastic plasma cells with cytologic atypia (bone marrow, Wright-Giemsa stain, ×1000). C,Plasma cells in the pleural fluid of a patient with plasma cell myeloma (Wright-Giemsa stain, ×1000).

Neoplastic plasma cells show an immunophenotype similar to that of their normal counterparts. At this terminal stage of differentiation, pan–B cell markers CD19 and CD20 and surface immunoglobulin chains are usually absent. Plasma cells are positive for CD138 (syndecan-1), high-density CD38 antigen, and monoclonal cytoplasmic immunoglobulins. These monoclonal proteins, in the form of complete immunoglobulin—most commonly IgG or IgA or isolated clonal light chains—are secreted by the neoplastic plasma cells and are seen in serum and urine as monoclonal spikes. In addition, neoplastic plasma cells can show an expression of other antigens typically not expressed by normal plasma cells, such as CD56 and myeloid markers.

Clinical features and prognosis. 

Plasma cell myeloma is a disease of older individuals (median age, 70 years).30 Bone pain and pathologic fractures are directly related to the proliferation of neoplastic plasma cells. These cells produce factors that cause localized bone destruction (lytic lesions on radiographic examination) and hypercalcemia. Renal insufficiency is triggered by the obstruction or direct damage of renal tubules by monoclonal protein. Cytopenias are related to the replacement of normal trilineage hematopoiesis by massive plasma cell infiltrates. Depressed normal immunoglobulin levels result in a susceptibility to infections, which commonly occur in patients with plasma cell myeloma. High levels of serum immunoglobulins also may interfere with the coagulation cascade and impair circulation through an increase in serum viscosity. Tissue deposits of clonal immunoglobulins, called amyloidosis, may compromise kidney, heart, and liver function and cause peripheral neuropathies.

Most of the cases show a rapidly progressive course, and the median survival is 3 years. The prognosis is closely related to the number of plasma cells in the bone marrow and to clinical features reflecting overall tumor burden. Patients with more than 50% bone marrow plasma cells, associated renal failure, and severe anemia have a shorter survival than patients with fewer than 20% plasma cells and preserved renal function.

Typically, patients with bone and extraosseous plasmacytomas are younger and respond favorably to local radiation therapy. Approximately 15% progress to plasma cell myeloma.

Asymptomatic monoclonal gammopathy (MGUS) occurs in fewer than 5% of individuals older than 70 years.29 As discussed earlier, 25% of patients with MGUS develop overt myeloma. That is why all individuals with MGUS should be monitored closely with repeat measurements of serum immunoglobulin levels and bone marrow examinations.

Diffuse large B cell lymphoma

Definition. 

The defining feature of DLBCL is the large cell size. In contrast to the neoplastic cells in the lymphoproliferative disorders discussed so far, DLBCL cells are significantly larger than normal lymphocytes. Most show a diffuse histologic growth pattern and can differ significantly in cytologic appearance and immunophenotype. DLBCL is one of the most common lymphomas, accounting for 30% to 40% of all non-Hodgkin lymphoma cases.9

Morphology and immunophenotype. 

The most common type, DLBCL not otherwise specified, shows a diffuse proliferation of large lymphoid cells replacing normal nodal architecture. Cells are at least twice the size of normal small lymphocytes and show single or multiple nucleoli and ample cytoplasm (). In rare cases, in addition to neoplastic large lymphoid cells, there is a considerable admixture of background histiocytes and small lymphocytes. Figure 36-19

Image 

FIGURE 36-19 Diffuse large B cell lymphoma with proliferation of large lymphoid cells. Note the size difference between small lymphocytes (arrow) and neoplastic B cells (arrowhead) (hematoxylin and eosin stain, ×500).

As in other B cell lymphomas, pan–B cell antigens are expressed. DLBCL can originate from a variety of stages in B cell development—hence the coexpression of other markers is heterogeneous. CD5, CD10, BCL6, CD30, and CD138 can be present (Table 36-2).

Clinical features and prognosis. 

Although, as with most lymphomas, the median age at diagnosis is in the sixties, DLBCL can be seen in children and young adults. Most commonly, it presents as a localized disease involving a group of lymph nodes. Bone marrow involvement is rare at presentation but can occur later in the course of the disease. DLBCL can also be seen in extranodal sites, including the gastrointestinal tract, central nervous system, bone, and serous effusions. DLBCL is an aggressive neoplasm with a proliferation rate frequently exceeding 40%, which makes it more sensitive to multiagent chemotherapy. The prognosis depends on a variety of clinical parameters, such as patient age, the extent of disease, and the site of involvement. The original morphologic subclassification of DLBCL was flawed by poor intraobserver and interobserver reproducibility.31 However, recent results of gene microarray studies have shown that patients with DLBCL of follicle center origin have better survival than patients with other subtypes.32

Burkitt lymphoma

Definition. 

Burkitt lymphoma is characterized by medium-sized, highly proliferating lymphoid cells with basophilic vacuolated cytoplasm. The WHO classification lists three variants of this lymphoma: endemic (occurring predominantly in Africa), sporadic, and immunodeficiency associated.

Morphology and immunophenotype. 

The lymphoid proliferation is diffuse and at low magnification shows a prominent “starry sky” pattern imparted by numerous tingible-body macrophages (, Figure 36-20 A). The macrophages are responsible for phagocytosing apoptotic debris, a by-product of the extremely high proliferative activity. Lymphoma cells are medium size with round nuclei, finely distributed chromatin, and small nucleoli. The cytoplasm is deeply basophilic and highly vacuolated, a feature best displayed on touch imprints or other cytologic preparations (Figure 36-20B).

Image 

FIGURE 36-20 Burkitt lymphoma. A, “Starry sky” pattern imparted by numerous macrophages with apoptotic debris (hematoxylin and eosin stain, ×400). B, Touch preparation showing characteristic cells of Burkitt lymphoma. Note the deeply basophilic cytoplasm with numerous vacuoles (Wright-Giemsa stain, ×1000).

The immunophenotype of Burkitt lymphoma reflects germinal center origin. CD19, CD20, CD10, and BCL6 antigens are present. There is surface expression of monoclonal immunoglobulin light chains. BCL2 is absent. The hallmark of Burkitt lymphoma is a high proliferation rate. Nearly 100% of Burkitt lymphoma cells are actively proliferating. This feature is linked to the constitutive expression of MYC gene (cell cycle gatekeeping gene) secondary to its translocation under the promoter of immunoglobulin heavy or light chain genes [t(8; 14), t(2; 8), or t(8; 22)]. This translocation is pathognomonic for Burkitt lymphoma, and its demonstration is required for a definitive diagnosis.

Clinical features and prognosis. 

The clinical presentation of Burkitt lymphoma is dependent on the variant (endemic, sporadic, or immunodeficiency associated). The endemic form presents in young children (4 to 7 years of age), most commonly as a jawbone mass. The sporadic variant, seen in the United States and Europe, occurs in children and young adults most commonly as an abdominal mass. Gastrointestinal tract and abdominal lymph nodes are often involved. Other extranodal sites, such as gonads and breasts, can be a site of primary disease. Immunodeficiency-associated Burkitt lymphoma presents most often as nodal disease. Independent of the presentation, Burkitt lymphoma commonly involves the central nervous system, bone marrow, and peripheral blood (Burkitt leukemia). Epstein-Barr virus (EBV) is present in a proportion of patients.

A diagnosis of Burkitt lymphoma is a medical emergency. Because of its high proliferation rate, the doubling time is extremely short. The chemotherapy is significantly different from that used for other types of high-grade lymphoma. These highly aggressive treatment regimens take into account the high proliferative activity and contribute to high cure rates for childhood and adult Burkitt lymphoma: 60% to 90%, depending on the stage of the disease.3334 Immunodeficiency-associated Burkitt lymphoma occurs predominantly in HIV-positive patients. Its prognosis is not as favorable as for other variants.

Mature T cell and natural killer cell lymphomas

Lymphomas derived from mature T cells and natural killer cells are much less common than the previously discussed mature B cell neoplasms and account for approximately 10% of all lymphomas. The incidence of the specific subtypes of T cell lymphoma shows geographic and ethnic variability. In certain geographic regions, T cell malignancies may be more prevalent than in the United States. Compared with B cell lymphomas, T cell neoplasms occur more frequently in extranodal sites. The most common skin lymphoma, mycosis fungoides, is of T cell phenotype.

Although morphology is an important criterion in the diagnosis of T cell lymphomas, a significant morphologic and cytologic variability is seen within specific subtypes. Similarly, the immunophenotypic features are not as specific as those seen in B cell malignancies. Due to the significant morphologic and immunophenotypic variability, an integration of morphologic, immunophenotypic, cytogenetic, molecular, and clinical information, as recommended by the WHO classification, is crucial in diagnosing T cell and natural killer cell malignancies. Until recently, the demonstration of clonality in T cell proliferations was limited to molecular methods showing T cell receptor gene rearrangements. The development of multiple antibodies directed against the variable region of the T cell receptor enables the determination of T cell clonality by flow cytometry.35

Mycosis fungoides and sézary syndrome

Definition. 

Mycosis fungoides is the most common cutaneous lymphoma. It is composed of small to medium-sized lymphoid cells with irregular nuclear outlines (cerebriform nuclei). These cells show a predilection for the epidermis (epidermotropism) and dermis and may spread to regional lymph nodes. Sézary syndrome presents as a disseminated disease with widespread skin involvement (erythroderma), lymphadenopathy, and circulating lymphoma cells (Sézary cells with characteristic cerebriform nuclei) (, Figure 36-21 A).

Image 

Image 

FIGURE 36-21 Mycosis fungoides. A, Sezary cell (Wright-Giemsa stain, × 1000) B, Dermal infiltrate of medium-sized lymphoid cells with angulated nuclei (hematoxylin and eosin stain, ×400). C, Neoplastic lymphocytes invading the epidermis (hematoxylin and eosin stain, ×400).

Morphology and immunophenotype. 

In mycosis fungoides, the extent of cutaneous infiltrate is related to the stage of the disease. Early lesions show patchy or lichenoid infiltrate of the dermis by small to medium-sized lymphoid cells with irregular nuclear outlines (Figure 36-21B). The aggregates of neoplastic lymphocytes in epidermis, called Pautrier microabscesses, are frequently seen in mycosis fungoides (Figure 36-21C). Later in the course of the disease, cutaneous infiltrates may become more dense and form tumor-like lesions. The involvement of regional lymph nodes and peripheral blood may be present, especially in advanced stages of the disease.

The immunophenotype is similar to that of T lymphocytes normally present in the skin. The expression of pan–T cell markers CD3, CD5, and CD2 is seen along with CD4 antigen. An important feature, rarely seen in benign lymphoid infiltrates, is the absence of CD7 antigen. The T cell receptor gene is clonally rearranged.

Sézary syndrome is by definition a disseminated disease with leukemic presentation and skin and lymph node involvement.3637 The malignant cells are medium size with cerebriform nuclei. Skin and lymph node involvement is more pronounced than in early stages of mycosis fungoides and shows diffuse, monotonous lymphoid infiltrates. Due to low interobserver reproducibility, the determination of peripheral blood involvement based purely on morphology is not recommended. Currently, both morphologic and immunophenotypic evaluations are performed in order to demonstrate at least 1000 Sézary cells/μL, a CD4-to-CD8 ratio of more than 10 (due to significant numbers of circulating CD4+ Sézary cells), and an aberrant immunophenotype.1 The latter is defined as a significant loss of CD7, CD26, or T cell marker(s) on CD4+ T cells.

Clinical features and prognosis. 

The incidence of mycosis fungoides increases with age, and the average age at presentation is 55 to 60 years. The survival of patients with early-stage disease is excellent, because progression and development of disseminated lymphoma are very slow.36 In this patient group, 10-year disease-specific survival was reported as 97% to 98%. In most cases, only local treatment is necessary. In contrast, Sézary syndrome is an aggressive lymphoma with a low (10% to 20%) 5-year survival rate.37

Peripheral T cell lymphoma, unspecified

Definition. 

Peripheral T cell lymphoma, unspecified, comprises a morphologically heterogeneous group of lymphomas with mature T cell phenotype.

Morphology and immunophenotype. 

Lymph node involvement is usually diffuse with a prominent vascular proliferation. The cytologic features are variable with medium-sized to large cells with atypical and occasionally pleomorphic nuclei (). Certain variants show a considerable admixture of reactive small lymphocytes, immunoblasts, histiocytes, and eosinophils. Bone marrow is frequently involved, but a significant circulating lymphoma component is rarely seen at presentation. Most cases are derived from CD4Figure 36-22+ T cells and retain this immunophenotype. Variable loss of pan–T cell antigens, including CD7, is seen.

Image 

FIGURE 36-22 Peripheral T cell lymphoma showing heterogeneous population of small, medium-sized, and large lymphoid cells (hematoxylin and eosin stain, ×500).

Clinical features and prognosis. 

Peripheral T cell lymphoma is an aggressive disease occurring predominantly in older adults (average age of 60 years). Generalized lymphadenopathy and a variety of constitutional symptoms, such as fever, night sweats, weight loss, and pancytopenia, are present at diagnosis. The 3-year survival rate is reported to be approximately 40%.38 Biologic features and advanced stage at presentation contribute to the dismal prognosis. In addition, few treatment regimens have been developed specifically for T cell lymphomas; aggressive B cell lymphoma protocols are commonly used to treat these disorders.

Anaplastic large cell lymphoma

Definition. 

Although considerable morphologic variability can be seen, a typical case of anaplastic large cell lymphoma is characterized by large atypical cells with pleomorphic nuclei and abundant cytoplasm. The expression of CD30 antigen and ALK-1 protein is seen in the majority of cases.

Morphology and immunophenotype. 

Numerous morphologic variants have been described, depending on the predominant architectural and cytologic features. The lymph node architecture is most often diffusely effaced by malignant lymphoid cells (, Figure 36-23 A). Occasionally, lymph node involvement may be partial with characteristic infiltrates of nodal sinuses. When significant fibrosis is present, anaplastic large cell lymphoma may resemble classical Hodgkin lymphoma. Regardless of the histologic variant, in almost every case, at least a proportion of cells are large with abundant cytoplasm and pleomorphic, eccentric, kidney-shaped nuclei, so-called hallmark cells. Leukemic involvement is not frequent, but it may be seen in the small cell variant. In such cases, the peripheral blood film shows atypical lymphoid cells with indented nuclei reminiscent of Sézary cells (Figure 36-23B). Immunophenotyping is instrumental for prompt diagnosis.

Image 

FIGURE 36-23 A, Anaplastic large cell lymphoma with large pleomorphic cells (hematoxylin and eosin stain, ×1000). B, Peripheral blood involvement by small cell variant of anaplastic large cell lymphoma (Wright-Giemsa stain, ×1000).

CD30 antigen and, in most cases, ALK-1 protein are defining immunophenotypic features of this lymphoma. The overexpression of ALK-1 is most often due to t(2; 5)(p23; 35) between the ALK-1 and nucleophosmin genes. Alternative partner genes for ALK-1 translocation have also been identified. The cytotoxic T cell origin of this lymphoma can be demonstrated by immunohistochemistry showing expression of cytotoxic antigens such as TIA-1, granzyme, and perforin.39 Pan–T cell markers (CD3, CD7, CD5) are often absent. The most commonly expressed T cell lineage–associated antigens are CD4 and CD2. Pan-hematopoietic antigen CD45 is expressed only in a proportion of cases (Table 36-4). By flow cytometry, the coexpression of myeloid markers such as CD13, CD33, and CD15 is seen in approximately 50% of cases. In cases negative for the T cell–associated antigens and ALK-1 protein, the demonstration of clonal T cell receptor gene rearrangement can help to render a definitive diagnosis.

TABLE 36-4

Immunophenotypic Features of Lymphomas Composed of Large Lymphoid Cells

Antigen

NLPHL

Classical HL

DLBCL

ALCL

CD30

+

+/−

+

CD15

+

CD45

+

+

+/−

CD20

+

+/−*

+

CD3

+/−

* If positive, the immunoreactivity is weak and present only in a proportion of neoplastic cells.

† Other T cell markers, such as CD2 and CD4, are more often present.

ALCL, Anaplastic large cell lymphoma; DLBCL, diffuse large B cell lymphoma; HL, Hodgkin lymphoma; NLPHL, nodular lymphocyte-predominant Hodgkin lymphoma.

Clinical features and prognosis. 

Anaplastic large cell lymphoma is less frequent in adults. However, it is one of the most common lymphomas in the pediatric population, representing 10% to 15% of childhood lymphomas. Anaplastic large cell lymphoma presents as disseminated nodal disease with constitutional symptoms. Extranodal sites, including skin, can also be involved. The most important prognostic feature is the expression of ALK-1 protein. ALK-1+ disease has a favorable prognosis, whereas ALK-1 disease shows survival rates more comparable to those of peripheral T cell lymphoma, unspecified.

Hodgkin lymphoma

Hodgkin lymphoma can be divided into two broad categories: nodular lymphocyte-predominant Hodgkin lymphoma and classical Hodgkin lymphoma.1 Although both disorders occur preferentially in young individuals and share certain morphologic characteristics, more recent studies have shown that they are biologically distinct entities, and they are discussed separately.

Nodular lymphocyte-predominant hodgkin lymphoma

Definition. 

Nodular lymphocyte-predominant Hodgkin lymphoma is a B cell neoplasm composed of relatively rare neoplastic cells (lymphocytic/histiocytic or “popcorn” cells) scattered within nodules of reactive lymphocytes.

Morphology and immunophenotype. 

The normal architecture of a lymph node is replaced by a nodular proliferation of small lymphocytes and scattered lymphocytic/histiocytic or popcorn cells, the latter being the neoplastic cells of nodular lymphocyte-predominant Hodgkin lymphoma (). These are large lymphoid cells with abundant cytoplasm and vesicular multilobated nuclei (popcorn nuclei). The nucleoli are inconspicuous. Figure 36-24

Image 

FIGURE 36-24 Characteristic popcorn (lymphocytic/histiocytic) cells of nodular lymphocyte-predominant Hodgkin lymphoma (arrow) (hematoxylin and eosin stain, ×1000).

The lymphocytic/histiocytic cells are of follicle center cell origin and are positive for B cell markers, including CD20 antigen, BCL6, and immunoglobulin chains (Table 36-4).40 The neoplastic cells do not show evidence of EBV infection. In addition to neoplastic cells, the nodules are composed of CD20+ small B cells, T lymphocytes, and CD21 positive follicular dendritic cell meshworks.

Clinical features and prognosis. 

Most patients are males in their thirties and present with localized peripheral lymphadenopathy. Mediastinal lymph node involvement is rare. As for classical Hodgkin lymphoma, the prognosis is excellent, with survival rates of 80% to 90% when the disease is diagnosed in the early stages.41

Classical hodgkin lymphoma

Definition. 

Classical Hodgkin lymphoma comprises a heterogeneous group of lymphoid neoplasms derived from the germinal center.42 It is characterized by the presence of relatively few diagnostic neoplastic cells, Reed-Sternberg cells, in a rich reactive background. The incidence of this disease varies in different geographic regions. In the United States and Europe, it is a common form of lymphoma occurring in young adults. In the United States, approximately 7400 new cases are diagnosed annually.5 A bimodal age distribution is observed, with incidence peaks between 15 and 34 years and older than 54 years.

Morphology and immunophenotype. 

On the basis of architectural features, the composition of the reactive background, and relative proportion of neoplastic cells, classical Hodgkin lymphoma can be divided into four subtypes (): Table 36-5

1. Nodular sclerosis

2. Mixed cellularity

3. Lymphocyte rich

4. Lymphocyte depleted

TABLE 36-5

Morphologic Subtypes of Classical Hodgkin Lymphoma

Subtype

Neoplastic Cells

Additional Morphologic Features

Nodular sclerosis

RS cells; Hodgkin cells; lacunar cells

Fibrotic bands; background of small lymphocytes, histiocytes, and eosinophils

Mixed cellularity

RS cells; Hodgkin cells

Background of small lymphocytes, eosinophils, neutrophils, histiocytes, plasma cells; no fibrotic bands

Lymphocyte rich

RS cells; Hodgkin cells

Diffuse nodular background of small lymphocytes; no or few eosinophils and neutrophils

Lymphocyte depleted

RS cells; Hodgkin cells

Numerous RS cells and Hodgkin lymphoma cells; few background lymphocytes

RS, Reed-Sternberg.

Reed-Sternberg cells are present in all subtypes of classical Hodgkin lymphoma. The typical Reed-Sternberg cell is large with a bilobed nucleus or two nuclei with prominent eosinophilic nucleoli and abundant cytoplasm (, Figure 36-25 A). When encountered in an appropriate background, Reed-Sternberg cells are pathognomonic for the diagnosis. However, not all neoplastic cells of classical Hodgkin lymphoma show the typical morphology of Reed-Sternberg cells. Variants of neoplastic cells, including Hodgkin cells, mummified cells, and lacunar cells, are often encountered in a single lymph node. Hodgkin cells are large mononuclear lymphoid cells with an oval nucleus, thick nuclear membrane, distinct eosinophilic nucleolus, and abundant cytoplasm. Mummified cells are degenerated or apoptotic cells with a pyknotic nucleus and condensed cytoplasm. Lacunar cells occur predominantly in the nodular sclerosis variant of classical Hodgkin lymphoma and are characterized by a lobated nucleus and artifactual retraction of cytoplasm secondary to formalin fixation. Because of this artifact, the cells appear to be situated in a clear space (i.e., lacuna).

Image 

FIGURE 36-25 Classical Hodgkin lymphoma. A, Typical Reed-Sternberg cells (arrows) of classical Hodgkin lymphoma with two nuclear lobes and distinct nucleoli (hematoxylin and eosin stain, ×500). B, CD30+ Reed-Sternberg cells and their variants (immunoperoxidase, ×500). C, Nodular sclerosis type of classical Hodgkin lymphoma showing broad fibrotic bands dissecting the lymph node (hematoxylin and eosin stain, ×40).

In all subtypes of classical Hodgkin lymphoma, Reed-Sternberg cells and their variants have a similar immunophenotype (Table 36-5). They are CD30+ in all cases (Figure 36-25B) and CD15+ in approximately 80% of cases. The CD15 immunoreactivity may be weak and seen in only a few malignant cells. The expression of B cell marker CD20 is weak to absent. Similarly, CD45 antigen is absent. The frequency of EBV infection depends on the subtype of classical Hodgkin lymphoma. The background small lymphocytes are predominantly CD4+ T cells.

Nodular sclerosis classical hodgkin lymphoma. 

The defining feature of the nodular sclerosis subtype is the presence of broad collagen bands transecting the lymph node and thickening of nodal capsule (Figure 36-25C). The background cellularity includes small lymphocytes, eosinophils, and histiocytes. This is the most common subtype of classical Hodgkin lymphoma, accounting for 70% of cases. The frequency of immunohistochemically demonstrable EBV infection is lowest in this variant.

Mixed cellularity classical hodgkin lymphoma. 

In the mixed cellularity subtype, Reed-Sternberg cells and their variants are scattered among the diffuse background composed of small lymphocytes, histiocytes, eosinophils, neutrophils, and plasma cells. Typical Reed-Sternberg cells, mononuclear Hodgkin cells, and mummified cells are seen; however, lacunar cells are absent. Similarly, fibrotic bands and capsular thickening are not present. Approximately 20% of classical Hodgkin lymphomas show this morphology. An association with EBV infection is seen in 75% of cases.

Lymphocyte-rich classical hodgkin lymphoma. 

In the lymphocyte-rich subtype, scattered mononuclear Hodgkin and Reed-Sternberg cells are seen together with a vaguely nodular background of small lymphocytes. Nodules represent remnants of mantle zones and germinal centers. Compared with other subtypes of classical Hodgkin lymphoma, the background cellularity is less heterogeneous.

Lymphocyte-depleted classical hodgkin lymphoma. 

The lymphocyte-depleted subtype is an uncommon variant of classical Hodgkin lymphoma occurring predominantly in immunodeficient patients. There is a paucity of reactive background, and neoplastic Reed-Sternberg cells and their variants are much more frequent. In most cases, neoplastic cells show evidence of EBV infection.

Clinical features and prognosis. 

With the exception of the lymphocyte-rich variant, which occurs in a slightly older population, classical Hodgkin lymphoma is a disease of young adults with a peak incidence at 15 to 35 years. Mostly peripheral lymph nodes are involved, except in the nodular sclerosis variant, which often shows mediastinal lymphadenopathy. With the contemporary treatment protocols combining chemotherapy and radiotherapy, the cure rates are 80% to 90%, depending on the stage of the disease, patient age, and clinical symptoms. The best prognosis is seen in the nodular sclerosis subtype. Lymphocyte-depleted Hodgkin lymphoma is the most aggressive variant of classical Hodgkin lymphoma, especially in HIV-positive patients. In this patient group, Hodgkin lymphoma also may manifest in unusual extranodal sites, including bone marrow. Patients with classical Hodgkin lymphoma treated with a combination of chemotherapy and radiotherapy are at high risk of developing secondary malignancies, including lung and breast carcinomas and acute leukemia.

Summary

• Histologic components of normal lymph nodes include the cortex, paracortex, medullary cords, and sinuses. These are structural and functional compartments from which reactive hyperplasias and neoplasms originate.

• Lymphomas are neoplasms of the lymphoid system arising at specific stages of lymphoid differentiation.

• Modern lymphoma classification incorporates morphologic, immunophenotypic, molecular, laboratory data, and clinical characteristics.

• Lymphomas are broadly divided into neoplasms derived from precursor (immature) and mature lymphoid cells, and B cell and T cell malignancies.

• The most common mature B cell neoplasms are follicular lymphoma and DLBCL.

• The T cell neoplasms most common in the United States and Europe are peripheral T cell lymphoma, unspecified, and anaplastic large cell lymphoma.

• In CLL, the peripheral blood and bone marrow display smudge cells and small lymphoid cells with coarse chromatin, inconspicuous nucleoli, and scant cytoplasm.

• In HCL, small B lymphocytes have abundant cytoplasm and fine cytoplasmic projections.

• Hodgkin lymphoma has been shown to be of B cell origin.

• Hodgkin lymphoma is subclassified based on morphologic and immunophenotypic features.

• B cell and T cell lymphomas and Hodgkin lymphoma involve mainly lymph nodes; the involvement of extranodal sites and bone marrow or peripheral blood occurs with varying frequency.

• In general, lymphomas occur in elderly individuals; however, specific subtypes such as Hodgkin lymphoma show a predilection for younger age groups.

• The prognosis depends on lymphoma subtype. Indolent lymphomas show a protracted course but are largely incurable with current chemotherapeutic regimens. In contrast, aggressive lymphomas have a more rapidly progressive course, and the cure rates are higher.

Now that you have completed this chapter, go back and read again the case study at the beginning and respond to the questions presented.

Review questions

Answers can be found in the Appendix.

1. In most cases, the diagnosis of lymphoma relies on all of the following except:

a. Microscopic examination of affected lymph nodes

b. Immunophenotyping using immunohistochemistry or flow cytometry

c. Molecular or cytogenetic analysis

d. Peripheral blood examination and a complete blood count

2. The most common lymphoma occurring in young adults is:

a. Follicular lymphoma

b. DLBCL

c. Hodgkin lymphoma

d. Mycosis fungoides

3. In a normal lymph node, the medulla includes predominantly:

a. T cells

b. B cells

c. Tingible-body macrophages

d. Plasma cells

4. The t(11; 14) is the defining feature of:

a. Follicular lymphoma

b. Hodgkin lymphoma

c. CLL

d. Mantle cell lymphoma

5. The immunophenotype of mycosis fungoides is:

a. The normal T cell immunophenotype

b. An abnormal T cell immunophenotype with expression of CD4 and loss of CD7 antigen

c. A mix of CD4+ and CD8+ T cells

d. An abnormal T cell immunophenotype with expression of CD8 and loss of CD7 antigen

6. What is the major morphologic difference between Hodgkin lymphoma and other B cell lymphomas?

a. The extent of the lymph node involvement

b. The presence of numerous reactive lymphocytes and only a few malignant cells in Hodgkin lymphoma

c. The presence of numerous tingible-body macrophages in Hodgkin lymphoma

d. The preservation of normal lymph node architecture in Hodgkin lymphoma

7. Which morphologic diagnosis has to be confirmed with molecular studies demonstrating the presence of t(8; 14)?

a. Mantle cell lymphoma

b. Burkitt lymphoma

c. Follicular lymphoma

d. Sézary syndrome

8. What is the function of the germinal center?

a. Generation of B cells producing immunoglobulins with the highest affinity for a particular antigen through the process of somatic mutation

b. Production of plasma cells that secrete specific immunoglobulins following antigenic stimulation

c. T cell maturation following T cell education in the thymus

d. Generation of dendritic cells with unique antigen-processing capabilities

9. Marked paracortical expansion is most commonly seen in:

a. Rheumatoid arthritis

b. Syphilis

c. Dermatopathic lymphadenopathy

d. Follicular lymphoma

10. MGUS is best described as:

a. The presence of monoclonal immunoglobulin in serum with only mild bone marrow plasmacytosis

b. The presence of monoclonal serum or urine immunoglobulin with significant bone marrow plasmacytosis

c. The presence of significant bone marrow plasmacytosis in a patient with only a few clinical symptoms of plasma cell myeloma

d. The presence of monoclonal immunoglobulin in a patient with a solitary mass composed of plasma cells

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