Mohammed Z.H. Farooqui, Adrian Wiestner and Georg Aue
BACKGROUND
Chronic lymphocytic leukemia (CLL) is a disorder of morphologically mature but immunologically incompetent B lymphocytes and is manifested by progressive accumulation of these cells in the blood, bone marrow, and lymphatic tissues.1 CLL accounts for about 25% of all leukemia and is the most common leukemia in Western countries. Incidence increases with age from <1/100,000 individuals younger than 40 years of age to >20/100,000 in persons over age 65 and it is almost twice as frequent in men as in women. CLL is predominantly found in Caucasians and is rare in Hispanics and Asians. In 2011 there were 14,570 new cases of CLL in the United States, causing 4,380 deaths.2
ETIOLOGY AND PATHOGENESIS
CLL has historically been viewed as a disease of clonal B cells that have a low proliferation rate and a defect in apoptosis.1 CLL cells express the B cell receptor for antigen and antigenic stimulation of the clonal cells appears to be a major pathogenic driver. Recent work highlights the importance of proliferation that occurs primarily in the tissue microenvironment of the bone marrow and lymph nodes. Key pathways promoting CLL cell proliferation and survival in these tissues are activation of the B cell receptor and NF-kB pathways.3
A positive family history is one of the strongest risk factors for the development of CLL. There is an increased incidence of CLL with exposure to Agent Orange. Otherwise, no clear environmental factors predisposing to CLL have been identified.
CLINICAL MANIFESTATIONS
The most common initial manifestation of CLL is the incidental detection of lymphocytosis on a routine blood test or the presence of asymptomatic lymphadenopathy. Abdominal fullness, fatigue, reduced exercise tolerance, or other constitutional symptoms can also be presenting complaints. Symptoms can precede the onset of anemia or clinically manifest organomegaly. With advanced stage, patients may have recurrent infections, weight loss, or symptoms related to anemia and thrombocytopenia.
CLL can cause most of the signs or symptoms of non-Hodgkin lymphoma, specifically those related to B symptoms (night sweats, fevers, weight loss). The pace of disease is slower than in aggressive lymphomas, and the sudden onset of new symptoms, especially in previously untreated patients, should prompt efforts to exclude other diagnoses. Lymphadenopathy is typically nontender but lymph node enlargement can cause abdominal discomfort, fullness, and malaise. Even bulky lymphadenopathy rarely leads to obstruction or organ impairment. Splenomegaly is frequent and hepatomegaly due to CLL infiltration of the liver can occur. Extranodal involvement is not uncommon and can manifest as skin lesions or pulmonary nodules. Pleural infiltrations leading to effusions or gastrointestinal (GI) tract involvement leading to GI bleeding have been reported. Central nervous system involvement is unusual and neurologic symptoms should be investigated to determine other etiologies, especially infections. While night sweats or low-grade fevers can be symptoms of CLL, it is important to also consider infectious etiologies. Additionally, in CLL patients infections may lead to an exaggerated, albeit transient, increase in lymphadenopathy or splenomegaly, which needs to be differentiated from transformation into high-grade lymphoma.
DIAGNOSIS AND LABORATORY STUDIES
According to the International Workshop on Chronic Lymphocytic Leukemia (IWCLL) criteria a diagnosis of CLL requires the presence of >5 × 109 clonal B lymphocytes/L (5,000/µL) with a typical immunophenotype in the peripheral blood. Immunophenotyping or immunohistochemistry are required for diagnosis (see Immunophenotyping and Flow Cytometry). The World Health Organization classification of hematopoietic neoplasias describes CLL as a leukemic, lymphocytic lymphoma, being distinguishable from small lymphocytic lymphoma (SLL) only by its leukemic appearance.4 The diagnosis of SLL requires the presence of lymphadenopathy and/or splenomegaly but by definition clonal B lymphocytes in the peripheral blood are <5 × 109/L. While histopathologic evaluation of a lymph node biopsy may be the standard diagnostic test for SLL, the presence of circulating clonal B cells of typical immunophenotype may suffice in cases with an indolent presentation.
The presence of less than 5 × 109 clonal B lymphocytes per liter of blood in the absence of lymphadenopathy or organomegaly (as defined by physical examination or computerized tomography), cytopenias, or disease-related symptoms is defined as monoclonal B lymphocytosis (MBL). CLL is often preceded by MBL which progresses to CLL requiring treatment at a rate of around 1% to 2% per year.5 For the purposes of this chapter, the term “CLL” encompasses both CLL and SLL, and excludes MBL.
Complete Blood Count and Blood Smear
CLL cells are small, mature-appearing lymphocytes with round nuclei, clumped chromatin, and scant cytoplasm. Smudge cells, bare nuclei that appear squashed, are a classic feature. Prolymphocytes that are medium-sized cells with prominent nucleoli make up less than 10% of the lymphocytes in typical cases but may increase in proportion in rapidly progressive disease. Cases with more than 55% prolymphocytes are recognized as a distinct diagnostic entity called prolymphocytic leukemia (PLL). In advanced disease, anemia or thrombocytopenia is common, most often due to replacement of the bone marrow by tumor cells, with a possible contribution of hypersplenism or autoimmune mechanisms.
Immunophenotyping and Flow Cytometry
Flow cytometry is the single most informative diagnostic study in CLL. CLL cells are B cells (CD19 positive) that coexpress CD5 and CD23. These cells typically have weak expression of CD20, CD22, surface immunoglobulin, and are negative for FMC7, CD10, and CD103.
Bone Marrow Biopsy
Bone marrow is always involved in CLL and in the vast majority of SLL. Distinct patterns of infiltration, which have some prognostic value, are recognized: nodular, interstitial, diffuse, or mixed. Advanced disease is often associated with a diffuse pattern of infiltration. Bone marrow biopsy, outside of clinical studies, may be reserved for cases presenting diagnostic difficulties or those that have depressed peripheral blood counts. Immunohistochemistry on bone marrow or lymph node specimens can be used to assist in the diagnostic evaluation.
Lymph Node Biopsy
A lymph node biopsy can distinguish between CLL and other lymphomas or may be necessary to exclude transformation in patients with rapidly enlarging nodes, especially if the growth preferentially affects a single nodal area. The lymph node architecture in CLL is effaced by an abundance of small lymphocytes with clumped chromatin. Mitotic activity is typically low.
DIFFERENTIAL DIAGNOSIS
Morphology, flow cytometry, immunohistochemistry, and cytogenetics (see Prognostic Factors) are the tests with the best diagnostic yield. Briefly summarized in Table 14.1 are the main distinguishing features of closely related entities.
STAGING AND NATURAL HISTORY
The clinical course and the prognosis of CLL are extremely variable. Two staging systems have been used to risk-stratify CLL: the Rai classification (Table 14.2), utilized in North America, and the Binet classification commonly used in Europe. Both are based on clinical and laboratory parameters and confer prognostic information.
The Binet classification distinguishes three stages: stage A is characterized by fewer than 3 areas of lymphoid involvement, where the spleen counts as one lymphoid area; stage B involves 3 or more lymphoid areas; stage C is characterized by anemia and/or thrombocytopenia, regardless of the extent of lymphoid involvement.
IMAGING AND OTHER LABORATORY EVALUATIONS
Computed tomography (CT) is the imaging method of choice to determine the extent of lymph node involvement in CLL and to evaluate response to treatment. CT can identify Rai stage 0 patients with visceral lymphadenopathy, who have a clinical course similar to patients with Rai stage I.7 CLL lymph nodes typically have only weak metabolic activity on positron emission tomography (PET) even in extensive disease. While PET is not helpful in the diagnosis of CLL, it can add valuable information in advanced stage or relapsed disease when transformation into high-grade lymphoma is a consideration.
Other Laboratory Evaluations
Direct antiglobulin test (DAT) should be obtained prior to treatment and in patients with anemia. Conversion of the DAT from negative to positive may herald the onset of autoimmune hemolytic anemia (AIHA).
Serum immune globulins typically decrease with disease duration. Occasionally, a small M spike may be present.
Beta-2-microglobulin (B2M) may be elevated and often increases with disease bulk. High B2M levels (>3 mg/L) have been associated with inferior response to treatment.8 It is important to consider that renal insufficiency may also increase B2M.
LDH is typically normal. Elevated LDH is seen with AIHA and may be modestly increased in rapidly progressive disease. High LDH may be a sign of disease transformation.
A mild elevation of alkaline phosphatase is common. Elevated transaminases should trigger evaluation for viral hepatitis, especially if treatment with rituximab is considered.
PROGNOSTIC FACTORS
Several molecular markers have been identified that hold important prognostic information independent of clinical stage and are therefore particularly valuable in assessing early-stage patients. These markers primarily predict the pace of disease progression in untreated patients and overall survival (OS). In contrast, factors that predict response to treatment are, at present, incompletely defined9,10 but include del 17p, high B2M, and advanced disease.
Immunoglobulin Variable Region Heavy Chain Gene Mutation
The immunoglobulin (Ig) expressed by B cells is composed of light and heavy chains encoded by distinct genes. The presence or absence of somatic mutations in the variable region of the heavy chain gene (VH) distinguishes between two disease subsets: patients whose CLL cells express unmutated immunoglobulin variable region heavy chain (IGHV) genes (Ig-unmutated CLL) have a shorter survival than patients whose CLL cells express mutated genes (Ig-mutated CLL). Ig-mutated CLL can have a median survival of 20 or more years, typically a stable or slow progressive course, and may never require treatment. In contrast, Ig-unmutated CLL is more rapidly progressive, typically requires treatment within a few years from diagnosis, and is associated with a shorter median survival of 8 to 10 years.11
ZAP-70
The tyrosine kinase ZAP-70 is essential for T cell receptor signaling in response to antigen. ZAP-70 is highly expressed in T and NK cells and may be expressed in activated B cells. Relatively higher expression of ZAP-70 is typically seen in Ig-unmutated CLL and infrequent in Ig-mutated CLL.12 ZAP-70 expression can be assessed by clinical flow cytometry and higher expression predicts more rapid disease progression as well as shorter OS. Time to treatment (TTT), measured as the time from diagnosis to treatment, is approximately 3 years in ZAP-70-positive CLL and reaches 9 years for ZAP-70-negative disease. Median OS in the two subtypes is about 9 years and can be as long as 25 years, respectively.13,14 ZAP-70 is a cytoplasmic protein that is expressed at levels lower in CLL B cells than in T cells, making the test technically challenging. Results close to the threshold should therefore be interpreted with caution.
Cytogenetics
Due to the low mitotic rate of CLL metaphase chromosomal studies using G banding are often not informative. To evaluate cytogenetic abnormalities in CLL, it is therefore necessary to use fluorescence in situ hybridization (FISH). FISH can identify abnormalities in approximately 80% of cases. In a pivotal study, chromosome 13q deletion was present in 55%, deletion of 11q in 18%, trisomy 12 in 16%, and deletion 17p in 7%. No karyotypic abnormality was detected in 18%. Several other abnormalities were found less frequently, and 29% of patients had two or more aberrations.15 These lesions are not CLL specific and their detection is more informative for prognosis than diagnosis. Currently considered a research test, whole genome sequencing so far has identified several genes that are mutated in up to 20% of untreated CLL patients including TP53, ATM, MYD88, NOTCH1, SF3B1, ZMYM3, MAPK1, FBXW7, DDX3X.16
Deletions of chromosome 17p (p53 locus) or 11q (ATM locus) are associated with inferior outcome: median survival in these patients has been estimated at 32 months for 17p deletion and 79 months for 11q deletion. However treatment-naive patients in whom tumor cells with 17p deletions make up <25% of the clone have a rate of progression that is not significantly different from patients without this abnormality.17 The longest OS of 133 months has been associated with an isolated 13 q deletion.9,15 Because many patients may have more than one abnormality, a hierarchical model of genetic subgroups has been proposed, which assigns patients to the genetic subgroup of the prognostic dominant abnormality. For example, a combination of 13q deletion and 17p deletion is assigned to the prognostic group of 17p deletion; 17p deletions are relatively infrequent in newly diagnosed patients but are more common in relapsed or refractory disease. 17p also correlates with poor treatment response to chemotherapy.9
CD38
Increased CD38 expression on the cell surface of CLL cells as measured by flow cytometry correlates with inferior outcome.18 CD38 expression is a partial surrogate for the Ig-gene mutation status and/or ZAP-70 expression in some studies but not others.
Lymphocyte Doubling Time
A lymphocyte doubling time (LDT) of less than 12 months indicates more rapidly progressive disease and is associated with decreased survival independent of stage. LDT < 6 months is a feature of active disease and may be an indication to consider treatment.
TREATMENT
When? The Paradigm of Watchful Waiting
Most patients with early-stage CLL are asymptomatic and have a relatively good long-term prognosis. Several randomized trials investigating immediate versus deferred chlorambucil-based treatment in early-stage patients showed a slightly inferior survival with immediate chemotherapy.19 Deferral of treatment or “watchful waiting” has therefore become the standard of care for patients with early-stage CLL. Periodic evaluation including basic laboratory testing at 3-to-6-month intervals is a reasonable strategy for asymptomatic patients with relatively stable disease. Treatment is reserved for symptomatic or rapidly progressive disease.20 Guidelines notwithstanding, over the past decade it appears that patients are increasingly treated at earlier stages of disease, despite the absence of data demonstrating that this approach is of long-term benefit.
According to the IWCLL criteria4, active disease should meet the following:
Constitutional symptoms due to CLL (fevers, night sweats, weight loss)
Symptomatic/massive (>10 cm) lymphadenopathy
Symptomatic/massive splenomegaly (>6 cm below costal margin)
Progressive marrow failure: worsening anemia and/or thrombocytopenia
Rapidly progressive lymphocytosis (lymphocyte doubling time <6 months)
Autoimmune cytopenias (ITP, AIHA, PRCA) poorly responsive to corticosteroid treatment
How? An Increasing Choice of Active Agents
Alkylating Agents
Prior to the introduction of purine analogues, oral chlorambucil was the drug of choice. Response rates between 40% and 80% were achieved.18 However, complete remissions to chlorambucil are rare and the response duration is short. It may still be considered in older patients with comorbidities when aggressive combination therapy is not an option.21 Cyclophosphamide is frequently used in combination therapies.8,10 Side effects include myelosuppression, nausea, and fatigue. Bendamustine has single agent activity in untreated CLL.22 Toxicities are similar to other alkylators.
Purine Analogues
The purine analogue fludarabine induced more complete responses and increased progression-free survival compared to chlorambucil in a randomized trial.23 There was no significant difference in OS, probably due to the crossover design of the study and the high response rate to fludarabine in patients who failed chlorambucil. Myelosuppression, with a nadir between days 12 and 16, lymphopenia, opportunistic infections, and the precipitation of autoimmune hematologic complications are among the main toxicities of fludarabine. Prolonged or repeated use of purine analogues can lead to severe suppression of hematopoiesis and protracted cytopenias. Other purine analogues, such as pentostatin and cladribine, are also effective in CLL, but these agents have been less extensively studied. Patients with no response to or relapse within 6 months of a fludarabine-containing regimen are considered fludarabine refractory.
Monoclonal Antibodies
Rituximab, a humanized anti-CD20 monoclonal antibody, is primarily used in combination regimens. Rituximab as a single agent at 375 mg/m2 weekly for 4 weeks can induce relatively short partial responses in about 50% of treatment-naive patients.24 Rituximab has more limited single agent activity in refractory or relapsed disease. Dose escalation studies found only minor increases in responses that remained short lived. The first infusion of rituximab often induces a systemic cytokine release syndrome that can be life threatening due to severe hypotension and bronchospasm. Premedication with antihistamines, slow infusion, and careful monitoring, especially during the first infusion have been helpful. Rituximab can be combined safely with chemotherapy. There is a slight increase in infectious complications; of special concern, treatment-related cases of progressive multifocal leukoencephalopathy (PML) caused by JC virus and reactivation of viral hepatitis have occurred.25 Ofatumumab is a second generation anti-CD20 monoclonal antibody that is fully humanized. The drug is approved for patients who are refractory to fludarabine and alemtuzumab. The pivotal ofatumumab trial had overall response rates of 58% in fludarabine- and alemtuzumab-refractory patients and 47% in fludarabine-refractory patients with bulky lymph nodes.26 Ofatumumab is now also being incorporated into combination therapy.
Alemtuzumab, a humanized anti-CD52 monoclonal antibody, is FDA approved for fludarabine-refractory and treatment-naive CLL. The pivotal trial found a response rate of 33% in fludarabine-refractory patients, mainly partial responses.27 Importantly, alemtuzumab was equally effective in patients with or without 17p deletions. However, the antibody appears to be less active in patients with bulky lymphadenopathy (>5 cm). Side effects include cytokine release syndrome, neutropenia, and pronounced lymphopenia, with an increased risk of opportunistic infections, making antimicrobial prophylaxis necessary. Alemtuzumab is associated with CMV reactivation and monitoring for CMV is recommended.
Purine Analogue Combination Regimens
The combination of fludarabine with rituximab induced more responses (84%) including more complete responses (CRs) (38%) than did fludarabine monotherapy in previously untreated patients.28 The combination of cyclophosphamide with fludarabine yielded superior response rates and better progression-free survival (PFS) than did fludarabine as a single agent.29,30 The addition of rituximab to cyclophosphamide and fludarabine (FCR, CLL8 trial) resulted in better PFS and overall response rates than cyclophosphamide and fludarabine alone.8,10 However, the combination with rituximab was more often associated with myelosuppression. There are other chemotherapies that are combined with rituximab, such as pentostatin and cyclophosphamide (PCR), or cladribine; however these options have not been shown to improve on FCR. Cyclophosphamide-containing combination therapies are associated with an increased risk of chemotherapy-related myeloid neoplasias.31 Therefore a case can be made to reserve cyclophosphamide for those patients who have deletion 11q, a group that is less responsive to fludarabine or FR regimens but responds very well to FCR.10 Patients with deletion 17p typically respond to FCR but responses are relatively shorter lived.
Allogeneic Stem Cell Transplantation
Allogeneic stem cell transplantation is potentially curative because of a potent graft-versus-leukemia effect. Non-myeloablative conditioning regimens are preferred over myeloablative conditioning, mostly because the first approach has less acute toxicity and is better tolerated in the elderly. Most studies report a transplant-related mortality rate of about 20% at 1 year and a long-term disease-free survival in the range of 50%.32 Allogeneic transplantation, especially for biologically fit patients with adverse disease features, such as fludarabine refractoriness or 17p deletion, should be considered and discussed early in the course of treatment and not considered only a last resort.
Treatment Considerations
Table 14.3 summarizes outcomes for different treatments in CLL. Comparisons between different studies are difficult as patient selection and disease stage affect outcome. Clearly there are better responses in earlier stage patients than in patients with advanced disease,8,30 and therefore lead time bias is an important confounder when comparing the efficacy of different treatment regimens outside of randomized studies. In addition, data on survival in many randomized trials is still too preliminary to allow firm conclusions. The effect of more intense treatment regimens on survival for all cytogenetic subgroups is therefore unproven. Treatment considerations should include patient fitness, comorbidities, and the side-effect profile of the chosen regimen. Commonly used first-line treatment choices for fit CLL patients are two or three agent combinations of fludarabine, rituximab, and cyclophosphamide: FR and FCR are typically repeated every 28 days for up to six cycles. High-risk patients (17p deletion) should be considered for aggressive chemoimmunotherapy or a clinical trial using new agents followed by allogeneic transplant if this is an option. Patients who are not suitable candidates for chemoimmunotherapy can be considered for oral chlorambucil.21
Patients with relapsed or refractory disease should be referred to clinical trials. In general, CLL patients benefit from being cared for by a hematologist/oncologist with CLL expertise, as OS has been shown to be almost 2 years longer for patients cared for by a CLL-hematologist than for patients seeing a hematologist/oncologist with expertise primarily in other areas.36 Patients who enjoyed a long remission with a fludarabine-based regimen may respond well again to a similar regimen, but repeated exposure to purine analogues carries an increased risk of severe myelosuppression. Fludarabine-refractory disease is defined by lack of response to purine analogue therapy or relapse within 6 months of achieving a response to such therapy.37 Such patients have poor survival prospects and may have adverse cytogenetic features (del17p or del11q) and/or have acquired p53 mutations. Additional effective treatment options include bendamustine, alemtuzumab, ofatumumab, allogeneic transplantation, high-dose methylprednisolone, and investigational agents such as B cell receptor signaling inhibitors (PCI 32765 or GS1101) or lenalidomide (Table 14.4).
Minimal residual disease (MRD) refers to small numbers of CLL cells that persist after treatment in patients who achieved a remission by standard criteria. MRD has recently become the focus of many clinical trials due to its predictive power for PFS. The eradication of MRD has been associated with longer PFS and, in some studies, OS.
Supportive Care
Supportive care in advanced CLL will often focus on cytopenias and infections. Intravenous immune globulin (IVIG) replacement infusions have some benefit to reduce incidence and severity of recurrent bacterial infections and are typically reserved for patients with frequent infectious episodes. The use of IVIG, however, has not been shown to improve OS.41 The protection conferred by vaccinations may be limited because of the immune defect in advanced disease. Live vaccines, such as, for example, the new herpes zoster vaccine, are contraindicated. Anti-infective prophylaxis against pneumocystis and/or herpes infections is not typically necessary with single-agent fludarabine but often part of combination regimens.8
COMPLICATIONS OF CHRONIC LYMPHOCYTIC LEUKEMIA AND THEIR TREATMENT
Autoimmune Manifestations
Autoimmune hematologic manifestations occur quite frequently in advanced disease or during treatment with purine analogues. AIHA and immune thrombocytopenia (ITP) are more common than pure red cell aplasia (PRCA) and autoimmune neutropenia is rare. These autoimmune complications often respond to prednisone or cyclosporine. Rituximab appears a particularly useful and directed therapy in patients in whom autoimmune disease arises during purine analogue treatment.42 Retreatment with purine analogues is generally not recommended because of the risk of recurrence and the potentially fatal outcome, especially with AIHA.
Infections
Infections from bacterial, viral, and fungal agents are the most important cause of morbidity and mortality in CLL. The most common infections are due to S. pneumonia, Haemophilus influenzae, and Herpeszoster. Immunosuppression secondary to chemotherapy and biologic agents, in particular alemtuzumab but also fludarabine, contribute to the increased incidence of infections. Prophylactic use of antibiotics in neutropenic or hypogammaglobulinemic patients is not recommended. Prophylaxis for pneumocystis and herpes infections is typically administered to patients receiving alemtuzumab or combination chemoimmunotherapies and may be especially beneficial in relapsed disease.27 G-CSF may be useful to reduce the duration of neutropenia associated with fludarabine combination regimens but should be used with caution as it may mask marrow toxicity of fludarabine that can result in persistent myelosuppression.
Richter Transformation
Transformation to an aggressive, high-grade, large B cell lymphoma or to a Hodgkin lymphoma is called Richter syndrome. Risk factors for the occurrence of Richter syndrome remain incompletely defined but its incidence does not seem to be increased as a result of prior treatment with fludarabine. Characteristic findings include systemic symptoms, rapid lymph node enlargement, elevation of LDH, and paraproteinemia. PET can be helpful in the diagnosis of Richter transformation. Treatment for Richter transformation is similar to high-grade lymphoma but the response to treatment is usually short lived.
SELECT INTERNET RESOURCES
Ongoing clinical trials: http://www.clinicaltrials.gov
Ongoing NHLBI clinical trials: http://patientrecruitment.nhlbi.nih.gov/Lymphoma.aspx
Education and patient information: http://www.clltopics.org
Research funding, education, and patient information: http://www.lymphoma.org
Patient run volunteer support groups: http://listserv.acor.org/archives/cll.html
Reference