Thoracic Pathology: A Volume in the High Yield Pathology Series 1st Edition

Follicular Dendritic Cell (FDC) Sarcoma

Definition

• Neoplasm arising in lymph nodes but also in extranodal sites from accessory cells of the immune system that are essential for the function of antigen presentation and germinal center reaction regulation

Clinical features

Epidemiology

• Very rare tumor

• Seen in adults; median age, 40 years

• Slight female predominance

Presentation

• Usually occurs in the lymph nodes but can also occur in other parts of the body involved with the immune system (e.g., thymus)

• Typically painless mass that grows slowly

• Some FDC sarcomas appear to be associated with Epstein-Barr virus and the hyaline–vascular type of Castleman disease

Prognosis and treatment

• FDC sarcoma was considered an indolent tumor; but recent larger reports with longer follow-up have showed that it is a more aggressive tumor and should be considered an intermediate-grade malignancy

• Local recurrence is seen in 50%, while distant metastases can occur in 25% of cases

• Treatment regimens vary widely; surgical resection is often included

Pathology

Histology

• Proliferation of atypical spindled to polygonal cells in a background of abundant small lymphocytes and plasma cells

• The nuclei are oval, with smooth contours, vesicular or granular chromatin, and distinct nucleoli

• The most common patterns are storiform, fascicular, and whorled, although tumors composed of plump cells often show a solid pattern

Immunopathology/special stains

• Follicular dendritic sarcoma cells generally share the same immunophenotype of nonneoplastic FDCs: CD21, CD35, and/or CD23 are the most specific diagnostic markers

• Other positive markers may include vimentin, fascin, HLA-DR, and EMA

Main differential diagnoses

• Nodular sclerosis classic Hodgkin lymphoma

  • Characterized by nodules composed of a mixed inflammatory cell infiltrate with scattered lacunar cell variants of Reed-Sternberg cells, separated by thick collagenous bands

  • Neoplastic cells show CD30 and/or CD15 immunoreactivity

• Primary mediastinal B-cell lymphoma

  • Younger adults

  • Sheets or irregular clusters of large cells with vesicular or hyperchromatic nuclei with irregular contours

  • Positive for B-cell markers

• Spindle cell thymoma

  • Characterized by bland epithelial and nonneoplastic lymphocytes that can, rarely, have a marked plasma cell infiltrate

  • The spindle cells are immunoreactive for cytokeratin, but negative for CD21 and CD35

• Thymic carcinoma (spindle cell variant)

  • The spindle cell variant of thymic carcinoma will show overt histological features of malignancy and complete loss of organotypic features of thymic differentiation

  • Lymphocytic infiltrate is usually not present

  • Keratin and often CD5-positive

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Fig 1 Follicular dendritic cell sarcoma. FDC sarcoma with diffuse proliferation of spindled to polygonal cells.

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Fig 2 Follicular dendritic cell sarcoma. The neoplastic cells are large and with atypical nuclei.

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Fig 3 Follicular dendritic cell sarcoma. The nuclei are vesicular and distinct nucleoli are present.

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Fig 4 Follicular dendritic cell sarcoma. Abundant lymphocytes and plasma cells are present in the background.

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Fig 5 Follicular dendritic cell sarcoma. This FDC sarcoma has spindle-shaped cells (A) and variable amount of lymphocytic infiltrates (B).

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Fig 6 Follicular dendritic cell sarcoma. Epithelioid FDC cells are more epithelioid in this sarcoma with prominent capillary network.

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Fig 7 Follicular dendritic cell sarcoma. Immunohistochemical staining for CD21 is strongly positive in the tumor cells.



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