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Current Approaches to Diagnosis and Risk Stratification in Chronic Lymphocytic Leukemia

Published Online: Jun 08,2017

Chronic lymphocytic leukemia (CLL) is a malignancy characterized by the clonal proliferation and accumulation of small, mature-appearing CD5-positive B lymphocytes in the blood, bone marrow, and secondary lymphoid tissues.1 A CLL diagnosis is established by the presence of more than 5x109/L peripheral lymphocytes co-expressing CD5, CD19, and CD23, and weakly expressing CD20, CD79b, and surface immunoglobulin.2 Small lymphocytic lymphoma (SLL), in which the same leukemic cell population is mostly restricted to the bone marrow and lymphoid tissues, represents a clinical variant of CLL and is similarly managed.3

 

CLL is the most common adult leukemia in Western countries. Its incidence increases with age, and with aging populations, its prevalence and mortality in Western countries will continue to rise. Improved diagnostic methods and more frequent blood testing have also led to increasing identification of early-stage CLL among younger patients.2,4 Approximately 10% to 15% of patients with CLL are younger than 55 years.2,4

 

Recent years have seen major advances in diagnostic approaches in CLL, and disease assessment may now include analysis of multiple genetic mutations in addition to recurrent cytogenetic changes.1 Furthermore, with the development of novel treatment approaches, the significance of prognostic markers is shifting. Awareness of current approaches to CLL diagnosis and assessment of disease criteria relevant to current risk stratification and treatment selection strategies is therefore prerequisite to tailor treatment for each patient.

EPIDEMIOLOGY AND RISK FACTORS

 

The incidence of CLL varies between geographic locations and is lower in Eastern Asian populations, such as China, Korea, and Japan, than in Western countries.1 Lower incidence of CLL is maintained in Asian individuals emigrating to Western countries and their progeny.5 With an age-adjusted incidence of approximately 4 per 100,000 inhabitants in Europe and the United States, CLL is the most common adult leukemia in adults in Western countries.2 In the United States, CLL accounts for approximately one-third of all annual new leukemia diagnoses (20,110 of 62,130 in 2017).6,7 According to estimates based on the US National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) database, CLL is most frequent in white populations in the United States (6.8 per 100,000 men and 3.5 per 100,000 women), followed by African Americans (4.9 per 100,000 men and 2.4 per 100,000 women).1,8 Rates are lower among Hispanic Americans (2.7 per 100,000 men and 1.6 per 100,000 women), Indigenous Americans (1.7 per 100,000 men and 1.3 per 100,000 women), and individuals of Asian or Pacific Island descent (1.7 per 100,000 men and 0.3 per 100,000 women) (FIGURE 11,8).

 

The risk for CLL increases with age (FIGURE 27). More than 70% of patients are older than 65 years at diagnosis, the median age at diagnosis is 72 years, and the incidence rate increases to >30:100,000/year at an age of more than 80 years.2 Men are at an approximately 2-fold higher risk for developing CLL than women (male:female ratio of 1.9).6

 

A genetic contribution to CLL susceptibility has been clearly established. Family members of patients with CLL have an 8.5-fold increased risk for developing the disease compared with the general population.9,10 Genome-wide association studies have identified polymorphisms in more than 25 loci associated with familial CLL, including candidate genes involved in B-cell biology, apoptotic pathways, and regulatory microRNAs that may contribute to disease development.11–14

 

Studies in veterans have established exposure to Agent Orange as an environmental risk factor for CLL.15 Insecticide exposure and farming history have also been associated with a higher risk for developing CLL,16 whereas blood transfusions and ionizing radiation have not.17,18

 

The precursor state to CLL, characterized as monoclonal B-cell lymphocytosis (MBL), is defined by the presence of less than 5000 monoclonal B cells, in the absence of lymphadenopathy, organomegaly, cytopenia, and clinical symptoms.2,19


 

 
Risk factors for MBL include increasing age and genetic disposition, including overlapping polymorphisms with those identified in CLL.19 Population studies have shown that MBL is characterized by a bimodal distribution of clonal B cell counts that can be cat- egorized as low-count and high-count MBL (less than or equal to or greater than 0.5x109/L clonal B cells, respectively). Low-count MBL rarely progresses to CLL, whereas the annual rate of progression from high-count MBL to CLL requiring therapy is 1% to 2%.20

 

 

EVOLVING METHODS OF CLL DIAGNOSIS

 

Many patients with CLL are asymptomatic and diagnosis follows the detection of lymphocytosis in a routine complete blood count (CBC), ie, above the normal adult upper limit of approximately 3500 cells per μL, typically ≥10,000 cells per μL.1 If disease symptoms are present, they may include fatigue, involuntary weight loss, excessive night sweats, abdominal fullness with early satiety, increased frequency of infections, and symptoms of an autoimmune cytopenia, as well as enlarged lymph nodes, hepatomegaly, and splenomegaly, which can be detected by palpation.1

 

Essential components of the CLL diagnosis include blood immunophenotyping by low cytometry and uorescence in situ hybridization (FISH), lymph node biopsy if a peripheral analysis is not sufficient, and absolute B monoclonal B lymphocyte counts.3 The initial workup should include a physical exam with palpation of node-bearing areas, determination of liver and spleen size, performance status, complete blood count, differential blood counts, platelets, and a metabolic panel.3

 

Immunophenotyping by low cytometry is required to establish CLL diagnosis based on cell identity, clonality, and quantity (<5x109/L peripheral CLL cells).2,3 CLL cells co-express CD5, CD19, and CD23 antigens, weakly express CD20, CD79b, and surface immunoglobulin, with each clone restricted to expression of either kappa or lambda immunoglobulin light chains, and are negative for cyclin D1. Flow cytometric analysis for these markers is therefore used to establish a differential diagnosis from other B-cell lymphoproliferative disorders such as marginal zone lymphoma, lymphoplasmacytic lymphoma, and mantle cell lymphoma (MCL), all of which express B-cell surface antigens, but usually do not express CD23 and have negative or low CD43 expression.2,3 MCL cells express CD5 but also exhibit enhanced expression of the gene encoding cyclin D1 (CCND1) due to the (11;14) translocation (t[11;14]), which is absent from CLL cells.1 As such, FISH analysis for t(11;14) can help to distinguish MCL from CLL.

 

CLL cells in blood smears are small, mature lymphocytes with a narrow rim of cytoplasm and a dense nucleus without detectable nucleoli and with partially aggregated chromatin. Smudged cells, also known as Gumprecht nuclear shadows, are also mor- phologically characteristic for CLL.4 Larger, atypical lymphocytes, cleaved cells, or prolymphocytes may be seen, but if the latter exceed 55%, prolymphocytic leukemia needs to be considered.1,21

 

Bone marrow biopsy is not considered essential for the diagnostic workup in CLL but may be needed if immunophenotyping results are unclear. According to the International Workshop of Chronic Lymphocytic Leukemia (iwCLL) 2008 guidelines for the diagnosis and treatment of patients with CLL, a bone marrow asipirate and biopsy may be desirable in both practice and prior to enrollment in a clinical trial (TABLE 1).21 If a biopsy is performed, 4 different patterns of infiltration may be observed, which are nodular, interstitial, mixed nodular/interstitial, or diffuse (advanced disease).1 Imaging using computed tomography (CT) scans can be beneficial for assessing the tumor load, monitoring disease progression, and determining the effects of investigational treatments in clinical trials, but it’s not recommended in asymptomatic patients or for staging.2,3



 

More than 80% of patients with previously untreated CLL have cytogenetic abnormalities, most commonly a deletion in chromosome 13q14.3 (del[13q]; 55%), followed by del(11q) (18%), trisomy 12 (16%), and (del[17p]) (7%), and del(6q) (6%).22 Recommended analyses include interphase cytogenetic analysis with FISH for the detection of the del(17p), which affects p53 expression, and if negative, molecular genetics is recommended for the detection of a TP53 mutation.2,3 While FISH testing for cytogenetic abnormalities is suggested for pretreatment evaluation by the iwCLL 2008 guidelines, the guidelines especially recommend these tests in patients being enrolled in clinical trials.21

 

Molecular genetic analysis should also include mutational status of the immunoglobulin heavy chain variable region gene (IGHV). Additional analyses considered informative for prognosis and treatment selection are stimulated metaphase analyses to identify complex karyotypes, extended FISH for additional cytogenetic abnormalities, and polymerase chain reaction or sequencing for mutations in NOTCH1, SF3B1, TP53, or MYD88.2,3

 


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Current Approaches to Diagnosis and Risk Stratification in Chronic Lymphocytic Leukemia
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