Khaled el-Shami and Bruce D. Cheson
The chronic leukemias have traditionally been grouped together to underscore their differences from the aggressive, acute leukemias. Chronic leukemias can be broadly divided into those arising either from mature lymphocytes or from hematopoietic stem cells or any of their nonlymphoid progenitors. The unifying feature among the chronic leukemias is that, initially, there is relatively normal maturation of the progeny of the neoplastic clone. Malignant hematopoiesis is effective and results initially in increased numbers of mature-appearing cells in the peripheral blood and bone marrow that have few morphologic abnormalities. Functionally, however, both chronic myelogenous leukemia (CML) cells and chronic lymphocytic leukemia (CLL) cells are less functionally competent than their nonleukemic counterparts. The relatively normal morphologic appearance is in marked contrast to the acute leukemias where maturation arrest with consequent bone marrow failure is the hallmark of the disease. Nonetheless, chronic leukemias have heterogeneous biology and natural history and may evolve into aggressive and difficult-to-treat phase(s) with ineffective hematopoiesis resulting in progressive marrow failure and organ infiltration.
I. CHRONIC MYELOGENOUS LEUKEMIA (CML)
CML is a relatively uncommon malignancy, accounting for 15% of adult leukemias in the United States. The annual incidence of CML is 1.5 cases per 100,000 with a slight male predominance. The median age at diagnosis is 53 years. Less than 10% of cases are under 20 years of age. Ionizing radiation is the only known risk factor. There is no known genetic predisposition or sociogeographic preponderance.
CML is a clonal hematopoietic stem cell disorder caused by a balanced translocation between the long arms of chromosomes 9 and 22 [t (9;22)(q34;q11), also known as the Philadelphia (Ph1) chromosome]. The hybrid BCR-ABL gene from the (9;22) translocation has been noted in almost all cases of CML and is considered pathognomonic. This BCL-ABL fusion protein results in constitutive tyrosine kinase signaling activity that mediates the biologic hallmarks of CML through activation of a mitogenic signaling pathways; altered cellular adhesion to the extracellular matrix; inhibition of apoptosis; and downstream activation of a complicated network of signaling pathways including RAS, mitogen-activated protein kinase, Myc, phosphatidylinositol 3 kinase, NF-k-B, and Janus kinase signal transducer and activator of transcription pathways.
The molecular pathogenesis in CML involves three different breakpoint regions in the BCR gene, resulting in distinct disease phenotypes. More than 90% of patients with CML express the 210-kDa oncoprotein, with a minority of patients expressing either a 185-kDa or 230-kDa oncoprotein without significant differences in the natural history of the disease.
CML is a triphasic process consisting of an indolent, chronic phase (CP) that lasts for several years prior to progression to a treatment-resistant accelerated phase, eventually transforming into a blastic phase (BP) similar to an acute leukemia, which is fatal in most cases. The finding in CML that the Ph1 chromosome is present in lymphoid, erythroid, as well as myeloid elements supports the idea that a neoplastic event involves a pluripotent stem cell.
Approximately 90% of patients with CML present in the CP of disease and may be entirely asymptomatic. Symptoms, when present, may include fatigue, bone aches, weight loss, and abdominal discomfort related to splenomegaly. The identification of a marked leukocytosis (usually greater than 25 × 109/L) due to a neutrophilia of all stages of maturation with a myelocyte “bulge” (i.e., myelocytes outnumbering the more mature metamyelocytes), lack of significant circulating blasts, absolute basophilia, frequent thrombocytosis, and mild anemia are key factors in the initial diagnosis. Leukocytes in patients with CML, while morphologically normal, exhibit a cytochemical abnormality with low leukocyte alkaline phosphatase (LAP) or neutrophil alkaline phosphatase when scored. The low LAP score is thought to be a consequence of relatively low levels of granulocyte colony-stimulating factor and is useful in differentiating CML from a reactive leukocytosis or “leukemoid reaction,” typically due to infection, in which the score is typically elevated or normal. Other less specific laboratory features include elevated elastase, lactate dehydrogenase, vitamin B12 (secondary to production of B12-binding protein haptocorrin by leukocytes), and uric acid levels. A bone marrow aspiration and biopsy is needed in all patients in whom CML is being considered, which will not only confirm the diagnosis, but also provide information necessary to stage and risk-stratify the disease. The bone marrow is invariably hypercellular with a myeloid-to-erythroid ratio in the range of 10 to 30:1. All stages of myeloid maturation are usually seen with myelocyte predominance. Megakaryocytes are increased in number and are characteristically smaller than normal. Up to 40% of patients will display increased reticulin fibrosis, which typically correlates with the degree of megakaryocytosis. Blasts usually account for less than 5% of the marrow cells, and more than 10% indicates transformation to an accelerated phase.
Up to 95% of patients with CML demonstrate the t(9;22) (q32;q11.2) reciprocal translocation that results in the Ph1 chromosome. The rest have either variant translocations, such as complex translocations involving other chromosomes or cryptic translocations of 9q34 and 22q11.2 that cannot be identified by routine cytogenetics. These are referred to as “Ph-negative” and require fluorescence in-situ hybridization (FISH) analysis to identify the BCR-ABL1 fusion gene, or reverse transcription (RT)-polymerase chain reaction (PCR) to identify the BCR-ABL1 fusion mRNA. Therefore, bone marrow samples of patients with suspected CML should be examined both by standard karyotyping (e.g., G-banded metaphase preparation) as well as interphase FISH. Of note, 10% to 15% of patients with CML harbor large deletions flanking the breakpoint on chromosome 9 and/or chromosome 22. Patients with such deletions have a shorter survival and time to progression to accelerated-phase (AP) or BP disease.
While the Ph1 is the initiating event in CML, progression to AP or blast crisis appears to require the acquisition of other non-random chromosomal or molecular changes (i.e., clonal evolution, which occurs in 50% to 80% of patients in the accelerated and blast crisis phases and, if noted during the chronic phase, confers a worse prognosis). The most commonly observed karyotypic abnormalities include trisomy 8, trisomy 19, duplication of the Ph1 chromosome, and isochromosome 17q (causing deletion of the P53 gene on 17p). Telomere shortening has also been associated with disease evolution. It is not known how these chromosomal changes contribute to the loss of cell differentiation that characterizes advanced-stage disease.
CML is characterized by three evolutionary phases, each carrying a different clinical and hematologic picture, natural history, and treatment outcome.
1. Chronic phase (CP) is the initial presentation of CML in approximately 90% of patients. This phase is marked by immature myeloid cells in the peripheral blood and marked granulocytic hyperplasia in the marrow; however, less than 10% of myeloblasts are present in both peripheral blood and bone marrow. Absolute eosinophilia and basophilia are commonly present (in contrast to reactive leukocytosis). The CP will typically run an indolent course of 3 to 5 years before progressing to the accelerated phase, even without treatment, although the duration can be highly variable.
2. Accelerated phase (AP) (Table 19.1) is poorly denned, but is usually marked by a loss of previously controlled white blood cell (WBC) counts and clonal evolution, with the development of new chromosomal abnormalities in addition to the persisting or re-emerged Ph1 chromosome. Peripheral blood counts show one or more of the following: blasts of at least 10%, basophils greater than 20%, or a fall in the platelet count to no more than 100,000μ, L, unrelated to ongoing treatment. These laboratory findings are often accompanied by the re-emergence or progression of symptoms such as fever, bone pain, and fatigue, or worsening splenomegaly. The median survival prior to imatinib therapy was only 18 months; however, with imatinib, the estimated 4-year survival rate exceeds 50%.
3. Blast phase (BP) (see Table 19.1), also called “blast crisis,” is the progressed transformation of CML to acute leukemia. It is defined by the acute leukemia criteria of at least 20% bone marrow blasts.
However, patients with 20% to 29% blasts seem to carry a better prognosis than those meeting the older criterion of greater than 30% blasts. A majority of cases (50% to 70%) will express a poorly differentiated myeloid phenotype (acute myelogenous leukemia [AML]), while the remainder shows lymphoid (pre-B acute lymphocytic leukemia [ALL]) or an undifferentiated or mixed-lineage phenotype. Recent studies have identified BCR-ABL kinase domain mutations in 30% to 40% of these patients. Persistence of the Ph1 chromosome including additional Ph1 chromosomes and other cytogenetic abnormalities may be present. Extramedullary tumor masses (chloromas) can occur in both the APs and BPs. Durable responses to chemotherapy, using various acute leukemia regimens, are typically uncommon, and median survival in this phase is 3 to 6 months. ALL evolutions in general have a better response and prognosis than AML evolutions. A CP remission can occur with treatment as the blastic progeny clone is eradicated, but the CP Ph1 stem cell typically persists. Transcription factor–induced aberrant lineage priming of leukemic stem cells can bring about variability in subsequenThevolution whereby patients achieving remission from a myeloid BP can re-enter a CP then relapse with a lymphoid BP (or vice versa).
Separation of these three stages is imprecise, and approximately 25% of patients progress directly from CP to BP. Although the duration of the CP is difficult to predict, a number of factors indicate an increased risk for progression, including greater age, splenomegaly, elevated platelet counts, and higher numbers of peripheral blood myeloblasts, eosinophils, or basophils. The Sokal prognostic system and the Hasford classification utilize a formula factoring in age, spleen size, and the hematologic picture to assign low, intermediate, and high groups differing in prognosis with 5-year survivals of 76%, 55%, and 25%, respectively. Both classifications were developed in patient cohorts receiving interferon, and none have thus far been validated during the imatinib era, limiting their usefulness. Regardless of pretreatment characteristics, the most important and best prognostic predictor of long-term survival is the quality of the response to treatment by minimal residual disease (MRD), which is measured by the degree of cytogenetic and molecular response.
Hydroxycarbamide (also known as hydroxyurea) is a ribonucleotide reductase inhibitor frequently used to control the high WBC count while confirming the diagnosis of CML. The usual dose of hydroxycarbamide is 40 mg/kg/d. The dose is then adjusted individually to keep the WBC count in a range between 4 and 10 × 109/L. Hydroxycarbamide does not reduce the percentage of cells bearing the Ph chromosome, and therefore, the risk of transformation to the BP is unchanged. Its use should be limited to temporary control of hematologic manifestations prior to starting definitive therapy. The “imatinib (Gleevec) era” has revolutionized the treatment of CML but also ushered in some questions of treatment uncertainty.
1. Imatinib (Gleevec) is a small molecule tyrosine kinase inhibitor (TKI) of the BCR-ABL tyrosine kinase. Targeting and inhibiting the BCR-ABL mitogenic pathway with imatinib has achieved dramatic cytogenetic and molecular levels of responses with prolonged disease control in CML. The most comprehensive source of information about the imatinib therapy for patients with CP disease is the IRIS trial. With a follow-up of 7 years, imatinib was discontinued for adverse events in 5% of patients and for lack of efficacy in 15% of patients. Seventy-five percent of patients with complete cytogenetic response (CCyR) have maintained the response so far. The 6-year event-free survival (EFS), progression-free survival (PFS), and overall survival (OS) rates were 83%, 93%, and 88%, respectively. Based on these results, 400 mg oral daily is deemed the standard initial dosing in CP disease. Maintaining imatinib dosing at greater than 300 mg daily is pharmacologically important to achieve effective inhibitory plasma concentrations. The results of the IRIS trial have been replicated in a prospective, multicenter German CML phase IV study, which reported a 5-year overall survival of 94% and a 2-year EFS of 80%. Studies addressing dose escalation of imatinib in early CP showed that 800 mg of imatinib was well tolerated and is associated with a high rate of cytogenetic and molecular responses, which are also attained more rapidly with the higher dose. However, whether such an approach results in long-term benefit or improvement in survival remains to be seen.
2. Imatinib can only control, and not completely eradicate, the CML clone, therefore being unable to cure the disease. Allogeneic stem cell transplantation is the only known curative therapy for CML. The question regarding the timing of transplant during CP CML remains controversial. However, it is clear that imatinib is the initiating therapy in treating CP CML and that close molecular monitoring of the BCR-ABL transcript is important to best manage an individual with CML.
3. Side effects of imatinib. Overall, imatinib is well tolerated. Side effects are generally mild and include nausea, peripheral and periorbital edema, muscle cramps, diarrhea, weight gain, and fatigue. Imatinib is metabolized through the CYP450 pathway, causing potential drug interactions. Rare organ damage can occur including liver toxicity, hypophosphatemia, and potential cardiotoxicity. Myelosuppression is the most common grade 3 to 4 toxicity, with neutropenia and thrombocytopenia during the first few months of treatment. These can be managed with growth factors or dose reductions; however, they may require discontinuation of the drug, which may be temporary or permanent.
4. Disease monitoring during imatinib therapy is used to assess for early hematologic treatment toxicity and to evaluate the ongoing and ultimate disease response, with the treatment goal of achieving MRD measured by a CCyR and a 3-log reduction molecular response (Table 19.2). A reasonable approach, modifiable to an individual patient and case, is as follows:
1. Complete blood count (CBC) weekly until stable, then every 4 to 6 weeks.
2. Marrow cytogenetics at diagnosis, at 6 and 12 months of initial treatment, and yearly with ongoing treatment.
3. Peripheral blood quantitative RT-PCR for BCR-ABL mRNA at diagnosis and every 3 months with ongoing treatment.
The timing and level of response are important management milestones. The earlier a cytogenetic and molecular response is achieved, the longer the ultimate response will last. A partial cytogenetic response (1% to 35% Ph-positive metaphases) by 3 to 6 months predicts an 80% to 95% likelihood of achieving an eventual CCyR. Quantitative PCR on peripheral blood is the monitoring method of choice. There is a significant correlation between the molecular response at 3 months and cytogenetic response at 12 months. At 42 months of follow-up, those patients with a CCyR by 12 months and a major molecular response (greater than 3-log reduction in BCR-ABL mRNA) had a PFS of 98% compared to 90% if less than 3-log reduction and 75% for patients without a CCyR. Tere is no absolute latest point in time at which a patient should have a CCyR before considering an altered treatment approach. Tat must be individualized based on age and other viable treatment options available. In a young patient who is a transplant candidate, if there is not an early optimal response within 6 to 12 months, consideration of this alternative therapy is appropriate.
5. Imatinib resistance can either be primary or secondary. Primary resistance without a complete hematologic response (CHR) occurs in approximately 5% of patients. Primary cytogenetic resistance (i.e., failing to achieve a partial cytogenetic response at 6 months or complete at 12 months) occurs in 15% of patients. After 42 months of follow-up, 16% of patients treated in the IRIS study developed secondary resistance or overtly progressed. In patients previously treated with interferon-α, 26% in CP developed resistance or progression. Imatinib resistance is much higher in APs (73%) and BPs (95%). When resistance is observed, a repeat bone marrow with cytogenetics and screening for the new kinase mutations should be performed to identify the T315I mutation, which is a marker of failure for all the currently available TKIs.
Strategies to overcome imatinib resistance remain challenging. Overt phase progression forces a treatment change, as the current therapy is ineffective. Mutation changes are clearly a harbinger of phase progression, but in a variable time frame. Imatinib dose escalation up to 800 mg can be attempted; however, tolerance and durability remain limiting factors. Switching to second-generation TKIs, either dasatinib or nilotinib (see subsequent discussion) is presently the standard of care for imatinib failure or resistance. The addition of conventional chemotherapy agents, either interferon or cytarabine, may also be considered if unacceptable toxicity to second-generation TKIs develop. An allogeneic stem cell transplant in eligible patients with imatinib resistance may be an additional option.
6. Alternative treatments
a. Dasatinib (Sprycel), a piperazinyl derivative that targets many tyrosine kinases, was selected for its potent inhibitory activity against Src and ABL kinases, including the active conformation of BCR-ABL1 and most mutated forms (except T315I). The drug was shown to be effective for the treatment of Ph+ leukemia and was approved for the treatment of patients with imatinib-intolerant and imatinib-resistant disease who have Ph+ CML in CP, AP, and BP. A prospective, randomized study of four different doses and schedules identified a dose of 100 mg once daily as an efficacious and well-tolerated dose. In patients with imatinib-intolerant disease in CP, the major cytogenetic response (MCyR) and the CCyR rates were 76% and 75%, respectively, with median time to MCyR being 2.8 months. In patients with imatinib-resistant disease in CP, the MCyR and the CCyR rates were 51% and 40%, respectively. The median time to CCyR and major molecular response was 5.5 months. In 80% to 90% of patients in CP, the responses were maintained for 2 years, the PFS was greater than 80%, and the OS was greater than 90%. In 150 patients with imatinib-resistant disease in CP, the results were superior in patients whose therapy was changed to dasatinib 70 mg twice daily compared with those in whom the imatinib dose was increased to 800 mg.
b. Nilotinib (Tasigna) Nilotinib is an aminopyrimidine derivative that inhibits the tyrosine kinase activity of the unmutated and several mutated forms of BCR-ABL (except T315I, and to a lesser extent Y253H, E255K, and E255V) with higher in vitro potency and selectivity than imatinib. Similar to dasatinib, nilotinib is effective for the treatment of Ph+ leukemias and was registered for treating imatinib-intolerant and imatinib-resistant patients with Ph+ CML in CP and in AP at a dose of 400 mg twice daily. In 194 patients in imatinib-resistant CP, the MCyR and the CCyR rates were 48% and 30%, respectively, whereas in imatinib-intolerant patients the respective rates were 47% and 35%. For all patients in CP, 1-year OS was 95%, and the proportion of patients remaining in MCyR after 1 year was 96%. Nilotinib was recently tested in a phase II study in upfront therapy of early CP at a dose of 800 mg daily showing a CCyR of 98% and a major molecular response of 70%. In a randomized trial, nilotinib was superior to imatinib as initial therapy and may become the new standard.
c. Allogeneic stem cell transplant. As mentioned previously, allogeneic transplantation remains the only known curative treatment for CML. The appropriate patient and the optimal timing of transplantation in CP CML remain controversial. To assist in patient selection, a transplantation risk score has been proposed by the European Blood and Bone Marrow Transplantation Group to assess both transplant-related mortality as well as long-term survival (Table 19.3). In most transplant series, a relationship appears to exist between the interval from diagnosis to transplantation and outcome (i.e., the earlier the disease at the time of transplant, the better the outcome). Five-year survival rates after myeloablative transplantation range from 60% to 80% in CP disease to 25% to 40% in AP and 5% to 10% in BP. It is appropriate to consider allogeneic transplantation at the first sign of drug therapy failure which, based on the IRIS study, is defined as lack of hematologic response by 3 months to first-line imatinib therapy, no cytogenetic response (Ph+ >95%) by 6 months, less than a partial cytogenetic response by 12 months (Ph+ >35%), and/or lack of CCyR by 18 months. Allogeneic transplant is the appropriate second-line therapy for suitable candidates with an available donor. Patients with advanced phases of the disease should also be considered for transplant as soon as a second CP occurs with either imatinib or a second-generation TKI with or without chemotherapy. Interestingly, prior treatment with TKIs does not negatively impact transplant-related toxicity or the outcome with allogeneic stem cell transplant. For patients without a human leukocyte antigen (HLA)-matched sibling, transplantation with a matched unrelated donor is an acceptable alternative. An important advance has been the development of techniques that permit molecular typing, which have demonstrated that only about 55% of individuals who are serologically identical are highly matched by molecular typing. Patients who receive transplants from molecularly matched donors have better outcomes. Fortunately, because of the relatively indolent nature of CML, adequate time is usually available to search for a matched unrelated donor through the National Marrow Donor Program and other donor registries. Age, disease stage at time of transplant, and degree of HLA matching all have been strongly correlated with outcome of transplant. For good-risk patients (age less than 40 years, first CP, and an HLA-matched sibling donor; see Table 19.3), leukemia-free survival of approximately 60% can be achieved. Reduced-intensity transplants have improved the outlook for older patients, particularly those older than 50 years of age or those with comorbid medical conditions.
Relapse following allografting can be managed with donor lymphocyte infusion (DLI), which results in molecular remissions within 3 to 12 months in as many as 60% to 80% of patients relapsing in CP and in up to 90% in those with molecular relapse. While the toxicity of DLI, including graft-versus-host disease (GVHD) and/or marrow aplasia, can be substantial, it continues to be the most effective therapy for relapse following stem cell transplant.
d. Interferon-α and cytarabine no longer have a role as primary therapy in CML given the results of the IRIS trial and availability of imatinib and second-generation TKIs. However, interferon-α, often in conjunction with low-dose cytarabine, has been shown in randomized clinical trials to result in improved 5-year survival ranging from 50% to 60% compared with busulphan and hydroxycarbamide. The combination of interferon-α and cytarabine achieve a 55% CHR and 15% complete clinical response. Importantly, half of the patients achieving a CCyR maintained it even after stopping interferon-α and may in fact be cured. As such, this combination can be used in patients who are resistant to all available TKIs (e.g., T315I mutation) either as the sole therapeutic modality or as a bridge to allogeneic stem cell transplantation.
7. Advanced-phase CML. It is conventional now to start treating patients who present in advanced phases (a term including APs and BPs) with a starting dose of imatinib at 600 to 800 mg daily; however, the response is more robust in CP of CML than in patients with advanced CML. Patients with “early” AP may obtain long-term responses to imatinib as a single agent, while those in blastic transformation (BT; BP) may have extremely short responses requiring a more aggressive initial strategy. Thus, they may be considered for treatment with dasatinib with its wider spectrum of activity against Src and Src family kinases. For patients in lymphoid BT, extrapolation from results obtained with treatment of Ph-positive ALL suggest that combining imatinib with standard ALL treatment may be the best initial approach. Once remission is achieved, maintenance treatment with cytotoxic drugs together with a TKI can then be continued. Neuroprophylaxis is also advisable. For patients presenting in myeloid BT, the combined use of a TKI with therapy appropriate to the AML induction regimen may be an optimal approach. Recently, dasatinib at 140 mg daily combined with daunorubicin and cytarabine has been shown to be well tolerated with induction of remission in half the patients and a median survival of 12 months. Unfortunately, even with aggressive treatment options, the probability of relapse in both lymphoid and myeloid BT remains high, and may be reduced by considering allogeneic stem cell transplantation while the patient is in remission. Transplantation during BP CML is associated with an approximately 80% risk of relapse with a 5-year survival of only about 5%. Thus, BT CML remains an extremely high-risk disease with a dismal prognosis, unlike CP CML; diligent molecular monitoring at more frequent intervals in these patients may help detect this disease phase earlier without delaying treatment.
In conclusion, for patients with CP CML, targeted therapies such as imatinib have changed the treatment paradigm. While transplantation remains the only curative approach for CML, the high response rates and tolerability of imatinib at 400 mg daily render it the standard treatment for patients with newly diagnosed CML. Other TKIs such as dasatinib or nilotinib are second-line agents. However, recent data suggest that even nilotinib may be more effective for the initial treatment of this disease. Allogeneic stem cell transplantation should be strongly considered in instances of drug therapy failure and for patients in AP or BP (typically following downstaging with drug therapy to a second chronic phase). While new treatment options for this disease continue to emerge, several unanswered questions remain: What is the optimal therapy for imatinib failure? What are the indications for allografting in the presence of second-generation TKIs? Should the second-generation TKIs be used in upfront therapy of early chronic phase? Should the mutational analysis guide the choice of TKI? Answers to these and other questions will be forth-coming as the algorithm for treatment of CML continues to evolve.
II. CHRONIC LYMPHOCYTIC LEUKEMIA (CLL)
CLL is the most common leukemia in Western countries with over 15,000 new cases projected in the United States in 2009. Tere are no evident etiologic factors, although there is a clear familial incidence with 10% to 15% of patients having a family history of a hematologic malignancy. Whereas more than half of patients are diagnosed over 70 years of age, about 10% to 15% of patients with CLL are younger than 50 years of age and 20% are younger than 55 years. Younger patients are more likely to die from CLL-related events, whereas older patients more often die from secondary malignancies and non-CLL causes.
A. Diagnosis and staging
In the World Health Organization classification, CLL and small lymphocytic lymphoma (SLL) are considered together as CLL/SLL, the distinction being the number of circulating B-cells with a threshold of5000/(μL. About half of the cases of CLL are asymptomatic at presentation and diagnosed incidentally.
1. Examination of a peripheral blood smear in CLL reveals a relatively homogeneous population of mature-appearing lymphocytes, with occasional smudge cells, occasionally with prolymphocytes that are larger with prominent nucleoli. The diagnosis of prolymphocytic leukemia (PLL) requires that greater than 55% of circulating lymphocytes are prolymphocytes. Other lymphoid malignancies that can be confused with CLL include hairy cell leukemia (HCL), marginal zone or follicular lymphoma, and T-cell leukemias.
2. The characteristic immunophenotype of CLL B-cells distinguishes this disease from these other entities: CLL cells are positive for CD19 and CD20 (generally dim), as well as CD23 and CD5, and are monoclonal with respect to expression of kappa or lambda light chains. Of note is that CD5/CD20+ B-cells can be detected in the peripheral blood of up to 5% of the normal population; this occurrence has been referred to as monoclonal lymphocytosis of undetermined significance, which, without other evidence of the disease, rarely evolves into CLL.
3. Staging of the patient with CLL includes assessment of renal and hepatic function, uric acid and lactate dehydrogenase, quantitative immunoglobulins, and a direct antiglobulin test (DAT). A bone marrow aspiration or biopsy is not needed to make the diagnosis; however, it is strongly recommended prior to therapy as it provides a baseline against which to compare the results of treatment and provides an assessment of the normal blood elements. A lymph node biopsy is rarely indicated in CLL unless there is a concern of Richter transformation. Whether computed tomography (CT) scans should be incorporated into routine practice is controversial. Patients with stage 0 CLL who have lymphadenopathy on CT have a greater likelihood of progressive disease.
a. Staging systems. For more than 30 years, CLL has been staged according to the classifications published by Rai, used in the United States, and Binet, applied in much ofEurope, which use physical examination and peripheral blood counts to separate patients into clinically meaningful risk groups (Table 19.4). The two systems have similar prognostic value.
Considerable heterogeneity in patient outcome within stages suggests the importance of other prognostic factors (Table 19.5). Over the past decade, there have been new important and clinically relevant insights into the genetics, biology, and immunology of CLL, which may predict the time to disease progression, requirement for therapy, and survival.
b. Cytogenetic abnormalities. FISH studies identify nonrandom chromosomal abnormalities in 80% of cases that are almost exclusively deletions or trisomy, without translocations. The most common abnormality is a 13q deletion, which occurs in about half of cases either alone or in combination with another abnormality. Normal karyotypes and trisomy 12 are the next in frequency followed by del(11q) and del(17p) (p53 mutation). There is a strong correlation between these findings and outcome; del(13q) confers a favorable prognosis, while normal cytogenetics and trisomy 12 have an intermediate outcome. The prognosis of patients with a del(11q) (mutation of ATM gene) is poorer. Those with a del(17p) (deletions or mutations in p53) and those with complex cytogenetic abnormalities generally exhibit a reduced likelihood of response to treatment and a poor survival. Cytogenetic abnormalities are not stable over time, and FISH might be repeated when there is a change in the clinical picture.
c. A number of other biomarkers have clinical implications. CLL can be distinguished into two groups based on the level of cellular differentiation as characterized by whether they exhibit an unmutated (or pregerminal center) or mutated (or memory B-cell) immunoglobulin heavy chain gene mutation (immunoglobulin variable region genes). The former is associated with a significantly worse outcome. Other potential surrogates for mutational status have been investigated. When the two cell populations were subjected to DNA microarray analysis, zeta-associated protein (ZAP)-70 is differentially expressed in the unmutated cells. Some studies suggest that ZAP-70 may even be a better predictor of outcome than mutational status. CD38 expression on CLL cells is also an independent, negative prognostic factor. There currently is no defined role for these new prognostic factors in the clinical management of patients with CLL. Moreover, some patients have a mix of high- and low-risk features. Tese biomarkers should be reserved for clinical trials to stratify patients among various therapies to better characterize their role in directing therapy.
B. Complications of CLL
1. Other malignancies. Long-term complications related to the disease or its treatment include an increased risk for common solid tumors including skin cancers and those of the gastrointestinal tract. Thus, patients should be encouraged to undergo routine screening for appropriate tumor types. In addition, about 15% of patients with CLL may transform to a more aggressive lymphoid malignancy including PLL and Richter syndrome, a diffuse large B-cell lymphoma that is particularly resistant to standard chemotherapy. Patients with CLL may also develop or even have coexisting AML, CML, ALL, and multiple myeloma.
2. Autoimmunity. At least 25% of patients will develop a positive DAT, but fewer than 5% develop autoimmune hemolytic anemia. Other patients may develop pure red cell aplasia. Immune thrombocytopenia is also a common consequence of the disease and its treatment. Tese consequences can often be successfully treated with corticosteroids or rituximab. Other immune complications are uncommon.
3. Recurrent infections. Patients with CLL are at an increased risk for infections as a consequence of hypogammaglobulinemia and abnormal activation of the complement system. Historically, the most common pathogens were those that require opsonization for bacterial killing, such as Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae. The increased use of immunosuppressive agents such as fludarabine and alemtuzumab has markedly increased the risk for infections with opportunistic organisms such as Candida, Listeria, Pneumocystis, cytomegalovirus, aspergillus, herpes infections, and others that were rarely encountered before the widespread use of these agents. Nevertheless, the use of prophylactic intravenous immunoglobulins is discouraged, as they are expensive, in short supply, have associated adverse reactions, and appear to protect patients from bacterial infections that are only mild to moderate in severity, not severe, and not viral or fungal infections. Thus, the administration of prophylactic intravenous immunoglobulins should be reserved for patients with recurrent bacterial infections.
C. Therapy of CLL
Most patients with CLL are asymptomatic at presentation. Randomized trials have failed to demonstrate an advantage to early intervention in such patients. Thus, watchful waiting is an acceptable approach, checking counts and performing a physical examination every 3 to 6 months. Indications for initiating therapy have been published by the National Cancer Institute (NCI)-sponsored Working Group, more recently reinforced by the International Workshop on CLL (IWCLL) recommendations, and include disease-related symptoms, massive and/or progressive lymphadenopathy or hepatosplenomegaly, recurrent infections, thrombocytopenia, or anemia. The decision to treat may be supported by a doubling of the lymphocyte count in a period of 6 months or less.
1. Initial therapy. Major changes have taken place in the initial therapy of CLL in recent years. Fludarabine-based therapy has replaced alkylating agent regimens, such as chlorambucil, as the standard initial treatment of CLL. Randomized trials have shown higher complete response (CR) and overall response rates with fludarabine compared to chlorambucil, with a longer time to progression, and even a survival advantage without an increase in secondary malignancies. The addition of cyclophosphamide to fludarabine improves the response rate and PFS compared with fludarabine alone, but without a survival benefit and with an increase in toxicities. Acceptable regimens include the following:
Fludarabine 25 mg/m2 intravenously (IV) over 10 to 30 minutes on days 1 to 5 every 28 days.
Fludarabine 30 mg/m2/day IV on days 1 to 3 and cyclophosphamide 250 mg/m2 IV on days 1 to 3, each given as separate 30-minute infusions; cycle is repeated every 28 days.
Chlorambucil may be used in the frail elderly, being well tolerated with minimal nausea and no alopecia. Various schedules are used, including daily oral doses of 2 to 6 mg by mouth with adjustments according to biweekly CBC.
2. Monoclonal antibody-based therapy of CLL. The availability of active and safe monoclonal antibodies has dramatically altered the treatment of CLL.
a. Rituximab. The first major advance in the treatment of CLL in many years was afforded by the availability of rituximab, a chimeric anti-CD20 monoclonal antibody that, as a single agent in patients with relapse or refractory disease, has limited activity, inducing about 15% partial remissions of brief duration, but with a 50% to 70% single-agent response rate in previously untreated patients. The potential role for this agent was first realized by Byrd and coworkers from the Cancer and Leukemia Group B who conducted a randomized phase II trial of concurrent versus sequential fludarabine and rituximab demonstrating an overall response rate of 90% with 47% complete remissions. Keating and coworkers developed the fludarabine, cyclophosphamide, and rituximab (FCR) regimen with a response rate of 95% including 72% complete remissions. In both studies, a survival benefit was suggested using historical controls. The German CLL study group (GCLLSG) recently provided data from the CLL-8 trial, a randomized phase III comparison of fludarabine and cyclophosphamide versus FCR for the initial treatment of 817 patients with CLL. They were able to demonstrate not only a significant prolongation of PFS (51.8 months versus 32.8 months), but also an apparent survival advantage for FCR as well (87.2% versus 82.5% at 3 years, p = 0.012). This study, and a second one in relapsed/refractory disease, confirms the role of rituximab in the treatment of this disease and led to the recent approval of this combination by the U.S. Food and Drug Administration (FDA) as initial treatment or for relapse. Whether FCR is indeed superior to fludarabine and rituximab (FR) is controversial. A phase III trial is currently comparing FR with FCR. The FR regimen is as follows:
Rituximab is given over three infusions during cycle 1, then once per cycle thereafter. Day 1 of cycle 1, 50 mg/m2 IV over 4 hours; day 3 of cycle 1, 325 mg/m2 IV, initially at 50 mg/hr, but escalating the rate as tolerated; day 5 of cycle 1, 375 mg/m2 IV over 1 to 2 hours. On days 1 of subsequent cycles (every 4 weeks), 375 mg/m2 IV over 1 to 2 hours for a total of six cycles.
Fludarabine 25 mg/m2/day IV over 30 minutes on days 1 through 5 of each treatment cycle, given after the rituximab on days it is given.
The FCR regimen is as follows. Note dose reductions for those 70 and older.
Rituximab is given over two infusions during cycle 1, then once per cycle thereafter. Day 1 of cycle 1, 50 mg/m2 IV over 4 hours; day 3 of cycle 1, 325 mg/m2 IV, initially at 50 mg/hr, buThescalating the rate as tolerated. On days 1 of subsequent cycles (every 4 weeks), 375 to 500 mg/m2 IV over 1 to 2 hours for a total of six cycles. (Nonstandard dose may require longer infusion.)
In patients younger than 70 years of age, fludarabine 25 mg/m2/day IV over 30 minutes on days 1 through 3 of each treatment cycle, given after the rituximab on days it is given. In patients 70 years of age and older, fludarabine 20 mg/m2/day IV over 30 minutes on days 1 through 3 of each treatment cycle, given after the rituximab on days it is given.
In patients younger than 70 years of age, cyclophosphamide 250 mg/m2/day IV over 30 minutes days 1 through 3 of each treatment cycle, given after the rituximab on days it is given. In patients 70 years of age or older, cyclophosphamide 150 mg/m2/day IV over 30 minutes days 1 through 3 of each treatment cycle, given after the rituximab on days it is given.
b. Alemtuzumab. The first antibody approved by the FDA for CLL was alemtuzumab, a humanized anti-CD52 monoclonal antibody. Alemtuzumab induces responses in 30% to 40% of patients with CLL failing after alkylating agents and fludarabine. The currently recommended schedule of administration for alemtuzumab is to escalate the dose from 3 mg as a 2-hour IV infusion on day 1 and, if tolerated, 10 mg as a 2-hour IV infusion on day 2, then 30 mg as a 2-hour IV infusion three times weekly as tolerated for up to 12 weeks. Because of an increased occurrence of Pneumocystis jiroveci (carinii) and herpesvirus infections, antimicrobial prophylaxis is essential, with weekly PCR for cytomegalovirus. The subcutaneous mode of administration appears to preserve activity with reduced fevers, rigors, and other toxicities. In a randomized comparison of alemtuzumab with chlorambucil in previously untreated patients with CLL, the antibody induced an overall response rate of 83.2% with 24.2% CRs, 7.4% of which were negative for MRD, compared with 55.4%, 2%, and 0%, respectively for chlorambucil. PFS also favored the alemtuzumab arm at 14.6 months versus 11.7 months. Toxicity was not substantially different between the arms.
c. Ofatumumab. Ofatumumab is a human anti-CD20 antibody that binds to a different epitope than rituximab. Ofatumumab has activity in patients with CLL who are refractory to fludarabine and alemtuzumab (FA-ref) or with bulky disease refractory to fludarabine (BF-ref), as the latter are not considered suitable candidates for alemtuzumab. In a study of 138 patients (59 FA-ref, 79 BF-ref), 63% of which had Rai stage III/IV disease and had received a median of five prior regimens, 59% of FA-ref and 54% of BF-ref patients had received prior rituximab. Ofatumumab was dosed at 300 mg IV at an initial rate of 3.6 mg/hour on day 1 followed 1 week later by 2000 mg for weekly doses 2 to 12 (see Chapter 33 for details). The overall response rate was 58% for the FA-ref group with a median PFS of 5.7 months, and 47% with 5.9 months in the BF-ref group. The median OS was 13.7 months and 15.4 months, respectively. Results were reported to be independent of prior rituximab therapy.
3. Bendamustine. One of the most active drugs in CLL is bendamustine, a bifunctional alkylating agent developed in East Germany in the 1960s. Following numerous reports of its activity in pretreated CLL, it was approved by the FDA for CLL based largely on a randomized trial demonstrating superiority over chlorambucil with respect to overall response rate (68% versus 31%), CRs (31% versus 2%), and median PFS (21.6 months versus 8.3 months), without a major difference in adverse effects. Because of its efficacy and tolerability, bendamustine is well suited for older patients. Moreover, it can be safely administered to patients with mild to moderate renal impairment without dose reduction.
Based on its impressive single agent activity (100 mg/m2 IV over 30 minutes on days 1 and 2 of a 28-day cycle, up to six cycles), the GCLLSG combined it with rituximab in 48 patients with relapsed and refractory disease and achieved an overall response rate of 77% with 15% CRs, and, notably, 78% of fludarabine-refractory patients responded. Based on these important results, they conducted the CLL-8 trial in 177 previously untreated patients. The 91% response rate with 33% CRs led to a randomized comparison in previously untreated patients against FCR in CLL-10, which could redefine the treatment for this disease.
4. Other new agents. New drugs with promise in CLL include lenalidomide (Revlimid), a second-generation immunomodulatory agent, which has been approved for patients with myelodysplastic syndrome and the 5q-chromosome abnormality, and for those with relapsed/refractory multiple myeloma. In two studies in patients with relapsed and refractory CLL, the response rate to lenalidomide was about 30% to 50%, with activity even in patients with unfavorable cytogenetics. Major side effects include tumor lysis syndrome and a flare reaction. Combinations with other agents such as rituximab or bendamustine are in development
Flavopiridol is a cyclin-dependent kinase inhibitor. In early studies, a lack of activity was observed in CLL. Byrd and coworkers treated 42 high-risk patients with a pharmacologically derived regimen of administration and achieved a 45% partial response rate lasting a median of greater than a year. Further development of this agent is under way.
5. Other agents. A number of small molecules that target the apoptotic pathways in clinical development include ABT-263 and obatoclax. Fostamatinib disodium inhibits the downstream effects of activation of the B-cell receptor and induces responses in half of patients with CLL/SLL.
6. Stem cell transplantation. Autologous stem cell transplantation has a limited role in CLL. The data on allogeneic BMT are primarily limited to younger patients with CLL and are associated with considerable morbidity and mortality. Submyeloablative preparative regimens may achieve successful engraftment without substantial acute GVHD; however, chronic GVHD has been a serious problem. Nevertheless, long-term disease-free survival can be achieved, and this option is promising, especially for younger patients who are refractory to their initial therapy or who have only a transient response to treatment.
7. Response Assessment in CLL. With the availability of effective treatments for CLL, standardized response criteria are essential. In 1988, the NCI-sponsored Working Group published the first widely accepted response criteria that were updated in 1996, and reinforced by the IWCLL in 2008 (Table 19.6). MRD eradication appears to be associated with prolongation of survival. Consolidation of response with agents such as alemtuzumab has been successful in eradicating MRD but with prohibitive toxicity.
III. RELATED B-CELL LEUKEMIAS
A. Prolymphocyte leukemia (PLL)
PLL may be of either B-cell or T-cell lineage. What was formerly called T-CLL or chronic T-cell lymphocytosis was renamed in the World Health Organization classification as T-PLL. Patients with B-PLL tend to be older than those with CLL, with a median age of 70 years at presentation. The main complaints include abdominal discomfort, fevers, and weight loss. Virtually all have advanced-stage disease at presentation, with a larger spleen and a higher WBC count, but less lymphadenopathy than CLL. PLL cells are large, with a round nucleus and a prominent nucleolus. In de novo PLL, most of the peripheral blood mononuclear cells tend to be prolymphocytes; in the setting of an aggressive transformation from CLL, there is a dimorphic population in the peripheral blood. The immunophenotype is different from CLL; the cells are positive for CD19, CD20, and CD24, and strongly express CD22, surface immunoglobulins, and FMC7. Fewer than a third express CD5 or CD23.
Patients with PLL tend to respond poorly to either single-agent or combination chemotherapy, with overall response rates of less than 25% and rare CRs. The median survival for de novo PLL is 3 years, and it is less than a year for T-PLL. Small series and anecdotal cases suggest activity for nucleoside analogs and alemtuzumab in PLL. Allogeneic stem cell transplantation should be considered for younger patients whose disease is responsive to induction therapy.
B. Hairy cell leukemia (HCL)
HCL is diagnosed in about 500 new patients each year in the United States, generally in older persons, with a strong male predominance. Patients generally present with symptoms referable to cytopenias. The most common signs include palpable splenomegaly (72% to 86%), hepatomegaly (13% to 20%), hairy cells in the peripheral blood (85% to 89%), thrombocytopenia (less than 100,000/(μL: 53%), anemia (hemoglobin less than 12/dL: 71% to 77%), and neutropenia (absolute neutrophil count less than 500/μL: 32% to 39%). The lymphocytes in the peripheral blood generally have an eccentric, spongiform, kidney-shaped nucleus, with characteristic filamentous cytoplasmic projections. The malignant cells express the B-cell antigens CD19, CD20, as well as the monocyte antigen CD11c, and specifically CD103. Bone marrow biopsy is generally required to confirm the diagnosis, as the aspirate is often not obtainable.
Treatment is indicated in the setting of massive or progressive splenomegaly, worsening blood counts, recurrent infections, greater than 20,000 hairy cells/μ L of peripheral blood, or bulky lymphadenopathy. Until the early 1980s, splenectomy was the standard treatment for HCL. Splenectomy is now reserved for the rare patient who is refractory to treatment and has splenomegaly that is either symptomatic or is resulting in cytopenias.
1. The purine analogs revolutionized the treatment of patients with HCL. Pentostatin (21-deoxycoformycin, DCF) at doses of 4 mg/m2 IV every other week for 4 to 6 months achieves CR in 60% to 89% of previously treated or untreated patients, including those who have failed interferon, with overall response rates of 80% to 90%. About 25% of patients have relapsed with more than 5 years of follow-up.
2. Cladribine. Using a 7-day continuous infusion or a 2-hour infusion for 5 to 7 days, cladribine (CdA) at 3.3 to 5.2 mg/m2 (see Chapter 33) achieves responses in 80% to more than 90% of patients, including 65% to 80% complete remissions. These responses tend to be durable, with 20% to 30% of patients relapsing with prolonged follow-up. In many cases, relapse is characterized only by an increase in bone marrow hairy cells, with no indication for treatment. Most patients who require retreatment achieve a second durable response.
The results with DCF are equivalent to those with CdA. The shorter duration of treatment makes CdA somewhat more attractive, although it may be associated with greater neurotoxic-ity and myelosuppression.
3. Rituximab has also shown promise for patients with HCL who fail purine analog therapy as it has an anti-CD22 pseudomonas exotoxin immunoconjugate.
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