Chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) is an indolent malignancy characterized by increased production of mature but dysfunctional B lymphocytes. CLL/SLL is defined as a monoclonal lymphoproliferative disease characterized by the proliferation and accumulation of morphologically mature but immunologically dysfunctional B-cell lymphocytes that are smudge cells, as noted on peripheral smear. The primary disease sites include peripheral blood, spleen, lymph nodes, and bone marrow. CLL and SLL are identical from a pathologic and immunophenotypic standpoint. Both CLL and SLL originate from B-cell lymphocytes but present with different manifestations depending on where the abnormal cells are found. Usually, the initial leukemic phase represents CLL, where the cells are present in the blood. This eventually progresses to the lymphoma phase, representing SLL, where the cells are found in the lymph nodes. The term SLL is commonly used to represent the lymphoproliferative process limited to the lymph nodes.
The exact etiology of CLL is unknown. Genetic factors, rather than environmental factors, are the most likely cause of CLL. However, few known risk factors for CLL include occupational causes by exposure to certain chemicals, radiation exposure, and tobacco users. Reports of farmers working around rubber manufacturing industries and workers with exposure to benzene and heavy solvent have shown an increased risk of CLL/SLL. However, these associations have not yet been proven. In atomic bomb survivors, no known increase in the incidence of CLL/SLL has been noted. However, there has been an increased risk of other types of leukemia. The uranium miner population, who suffer exposure to ionizing and non-ionizing radiation, has shown increased CLL incidence. Tobacco users and cigarette smokers show a significantly elevated risk of CLL compared to non-tobacco users. The Veterans Affairs recognizes CLL as having a relationship to exposure to Agent Orange or other herbicides during military service.
CLL comprises 25 to 30% of total leukemias in the United States. According to the American Cancer Society, there will be approximately 21,040 new CLL cases and about 4,060 deaths in the year of 2020. Worldwide, 191,000 cases and 61,000 deaths are attributed to CLL/SLL every year. CLL can affect adults as young as 30 years of age. However, it is mostly seen in adults with an average age of 70 years. CLL is extremely rare in children. The incidence is known to rapidly increase with increasing age. CLL has a slightly higher incidence in male populations than female populations (1.3 to 1 to 1.7 to 1). However, studies have shown that women can have a more aggressive form of the disease than men.
The incidence of CLL varies by geographic location and race. CLL is most commonly seen in adults of the Western population. It is high amongst the Caucasian population compared to the Asian Pacific Islanders or the African-American population. The incidence of CLL in Western countries is similar to that of the United States but is rarely seen in Asian countries (China and Japan). CLL is common amongst the Jews of Eastern European descent. It is most commonly seen in Non-Hispanic Whites and least common in Asians. The incidence in African Americans is in between the Caucasian and the Asian ethnicity groups.
CLL is reported to have a genetic basis and is known to run in families (familial CLL). The age at diagnosis of the second-generation offspring is nearly 20 years younger as compared to the parent. First-degree relatives (siblings, children, or parents) of CLL patients have double the risk for CLL. Moreover, 17% of first-degree family members of CLL patients had monoclonal B cell lymphocytosis, which is a precursor of CLL. Ultimately only a small percentage of patients with monoclonal B-cell lymphocytosis (MBL) will develop into CLL.
The pathogenesis of CLL/SLL is a two-step process that leads to the clonal replication of malignant B lymphocytes. The first step is the development of MBL cells secondary to multiple factors such as antigenic stimulation, genetic mutations, and cytogenetic abnormalities. The second step is the progression of MBL to CLL/SLL by the further insult to the B-cell clone, either due to additional genetic abnormalities or changes in the bone marrow microenvironment. B-cell antigen receptor (BCR) expression induces antigen-independent cell-autonomous signaling, which is an important step in the pathogenesis of CLL.
In CLL, CD5+ B cells are continuously activated by mutations leading to MBL. The accumulation of genetic abnormalities in more mature B cells causes a clonal division of the neoplastic B-cell within the lymph nodes. In CLL/SLL, the most common abnormal physical examination findings are lymphadenopathy, which is seen in 50 to 90% of patients. Cervical, supraclavicular, and axillary lymph nodes are the most commonly affected sites. These increased B-cell lymphocytes eventually spill into the peripheral blood leading to the detection of lymphocytosis on a CBC.
These neoplastic B cells escape apoptosis and continue to divide over time within the lymph nodes. They then infiltrate the spleen and bone marrow, causing splenomegaly and hypercellular bone marrow (on bone marrow biopsy). The splenomegaly leads to increase sequestration of RBCs and platelets, leading to anemia and thrombocytopenia by decreasing the RBCs and platelets. Patients are more susceptible to autoimmune hemolytic anemia (positive Coombs test) and autoimmune thrombocytopenia. These B cells eventually spread throughout the body, causing systemic symptoms such as fever, night sweats, unintentional weight loss, fatigue, and early satiety. Lack of functional B cells decreases the body's ability to produce antibodies for immune responses leading to hypogammaglobinemia, which eventually leads to an increased risk of infection.
Skin is the most commonly affected nonlymphoid tissue in patients with CLL. Leukemia cutis (skin lesions) mainly involves the face and manifests as papules, macules, plaques, ulcers, blisters, or nodules. Skin biopsy can help confirm the diagnosis of CLL. Nonspecific secondary cutaneous lesions may occur due to bleeding, vasculitis, and infection. Exaggerated reactions to insect bites have been reported in patients as well.
The first and foremost laboratory abnormality found in CLL is lymphocytosis in peripheral blood and bone marrow. The peripheral blood smear shows leukemic cells, which are small, mature lymphocytes with a darkly stained nucleus, condensed chromatin, and indistinguishable nucleoli with a narrow rim of basophilic cytoplasm. Classical "smudge" cells ("basket" cells) are also seen on peripheral blood smear; these are pathognomic of CLL. The smudge cells are more fragile than normal lymphocytes that are disrupted during the process of being spread on a glass slide.
Immunophenotypic analysis of the peripheral circulating lymphocytes by peripheral blood flow cytometry can be performed, which can help to diagnose CLL. Most cases of CLL can be identified using antibody specific panel for CD5, CD19, CD20, CD23, and immunoglobulin light chains. Characteristic CLL/SLL lymphocyte phenotype features include the following: low levels of immunoglobulins (most often IgM immunoglobulin and sometimes both IgM and IgD); expression of B-cell associated antigens (CD19, CD20, CD21, CD23, and/or CD24); and expression of CD5 which is a T-cell associated antigen. The most common immunophenotype expression of CLL/SLL is the coexpression of CD5, CD19, and CD23. As for the light chain immunoglobulins, only one type of light chain is seen, suggesting the monoclonality of the lymphocytes. However, in some cases, biclonal CLL expressing both light chains or different levels of expression of other immunophenotypic antigens is also seen.
Fluorescence in situ hybridization (FISH) is a highly sensitive test used to detect chromosomal abnormalities in patients with CLL/SLL. Cytogenetics evaluation of the peripheral blood smear with FISH for 17p. deletion, 11q. deletion, 13q. deletion and trisomy 12 is routine pretreatment evaluation of patients with CLL. Though all patients with symptomatic and advanced-stage CLL/SLL are treated similarly, patients with 17p. deletion or 11q. deletion requires special consideration.
17p. deletion causes CLL by TP53 mutation. TP53 is a tumor suppressor gene which is located on the short arm of chromosome 17. The normal "wild–type" TP53 gene activation occurs in response to damaged DNA and/or other stressors such as hypoxia, leading to cellular apoptosis. The deletion/point mutation of TP53 leads to CLL. 11q chromosome contains the ataxia-telangiectasia mutated (ATM) gene. ATM kinase is responsible for the delayed progression of the cell cycle in the presence of DNA damage, allowing the cell to repair the damage. ATM kinase phosphorylates tumor suppressor p53 protein in the presence of DNA damage. The phosphorylation of p53 protein ultimately leads to cell cycle arrest/apoptosis of cells with DNA damage. In the absence of ATM kinase in 11q. deletion, phosphorylation of p53 does not occur, which hence cannot prevent the cell cycle arrest in DNA damaged cells.
Patients with CLL are often asymptomatic at the initial presentation, when a routine CBC reveals abnormal lymphocytosis, leading to CLL diagnosis. Approximately 5 to 10% of patients with CLL are symptomatic with B symptoms such as Fever of > 100.5 degrees F for > 2 weeks with no evidence of infection; unintentional weight loss >/= 10% of body weight over the last 6 months; drenching night sweats with no evidence of infection; extreme fatigue; and early satiety.
Upon physical examination, 50 to 90% of the patients with CLL present with localized/generalized lymphadenopathy. The most common sites include cervical, supraclavicular, and axillary lymph nodes. On palpation, the nodes are firm, non-tender, round, and freely mobile. Splenomegaly is the second most commonly enlarged lymphoid organ, seen in 25 to 55% of cases. On palpation, it is painless on non-tender with a smooth, firm surface. Hepatomegaly is seen in 15 to 25% cases. The liver is mildly enlarged and palpated 2-6 cm below the right costal margin. On palpation, the liver is firm and non-tender with a smooth surface.
Skin examination is an important part of physical examination because skin cancers are a relatively frequent CLL complication. Skin is the most common non-lymphoid tissue involved in patients with CLL. Leukemia cutis (skin lesions) mainly involve the face and manifest as papules, macules, plaques, ulcers, blisters, or nodules. Skin biopsy can help confirm the diagnosis of CLL. Nonspecific secondary cutaneous lesions may occur due to bleeding, vasculitis, and infection. Exaggerated reactions to insect bites have been reported in for patients as well.
Infiltration of the spleen and bone marrow with neoplastic B cells causes splenomegaly and hypercellular bone marrow. The splenomegaly leads to increased sequestration of RBCs and platelets, leading to anemia and thrombocytopenia by decreasing the RBCs and platelets. Patients with anemia are symptomatic with fatigue and shortness of breath; patients with thrombocytopenia easily bleed/bruises, and petechiae can be seen on physical examination. Lack of functional B cells decreases the body's ability to produce antibodies for immune responses leading to hypogammaglobinemia, which eventually leads to an increased risk of infection.
The first step in the diagnosis of CLL is a peripheral blood smear. The peripheral blood smear shows an absolute lymphocyte count of greater than 5000/mcL and smudge cells that confirm CLL. Although the diagnostic criteria for CLL are >=5000/mcL B lymphocytes on peripheral smear, a large proportion of patients present with an absolute lymphocyte count > 100,000/mcL. In patients with SLL, peripheral blood smear shows an absolute lymphocyte count of less than 5000/mcL along with lymphadenopathy but without cytopenias. However, lymph node biopsy is required to confirm the diagnosis of SLL.
Immunophenotypic analysis of the peripheral circulating lymphocytes by peripheral blood flow cytometry can be performed, which can help confirm the clonality of circulating B cells in CLL patients. Flow cytometry can be performed on both peripheral blood and bone marrow aspirate to look for the classical immunophenotypic markers of CLL. To reiterate, characteristic CLL/SLL lymphocyte phenotype features include low levels of immunoglobulins (most often IgM immunoglobulin and sometimes both IgM and IgD); expression of B-cell associated antigens (CD19, CD20, CD21, CD23, and/or CD24); and expression of CD5 which is a T-cell associated antigen. The most common immunophenotype expression of CLL/SLL is the coexpression of CD5, CD19, and CD23. However, different levels of expression of other immunophenotypic antigens are also seen. Serum immunoglobulins and free-light chains are measured at baseline to assess the immunodeficiency and during treatment, to look at immune reconstitution, especially with the newer generation B-cell receptor signaling drugs. As for the light chain immunoglobulins, only one type of light chain suggesting the monoclonality of the lymphocytes. Rarely, some patients express both kappa and lambda light chains, known as "biclonal CLL."
FISH is a highly sensitive test used to detect chromosomal abnormalities in patients with CLL/SLL.
Although not needed for diagnosis, bone marrow aspiration and biopsy are often done as a part of a diagnostic workup or before treatment. If the biopsy specimen demonstrates greater than 30% lymphocytes of all nucleated cells in a normocellular/hypercellular bone marrow aspirate, this confirms the diagnosis of CLL. The reduction of lymphocytic infiltration to less than 30% on treatment indicates a complete response. Furthermore, three infiltrative patterns of lymphocytes have been recognized in the bone marrow biopsy specimens: nodular, interstitial, and diffuse. A biopsy sample can demonstrate a mixture of nodular and interstitial, or nodular and diffuse patterns. Studies have shown that patients with a diffuse pattern on biopsy tend to have advanced disease with poor prognosis, whereas nodular and interstitial patterns ("non-diffuse" category) have a better prognosis.
Excisional lymph node histology demonstrates diffuse effacement of nodal architecture along with some scattered residual likely germinal centers. These lymph node infiltrates are predominantly composed of small lymphocytes. However, large lymphoid cells, such as pro-lymphocytes, are always present in clusters and are known as " pseudo-follicles" (proliferation centers), a pathognomic finding, and CLL/SLL patients. Spleen histology demonstrates the infiltration of red and white pulp with a more prominent white pulp involvement compared to red pulp. From an imaging standpoint, a CT scan helps in evaluation to see the degree of lymphadenopathy and organ infiltration in the form of spleen and liver sizes.
Diagnoses of complications of CLL such as autoimmune hemolytic anemia involves a positive direct antiglobulin (Coombs) test, increased reticulocyte count, elevated serum LDH, reduced haptoglobin, and elevated serum indirect bilirubin. Diagnosis of further complications such as pure red cell aplasia and thrombocytopenia can be made by a peripheral blood smear and a bone marrow aspiration and biopsy. Hypogammaglobulinemia (less than 15% of cases), elevated uric acid level and elevated hepatic enzymes are other findings seen in CLL. Important lab studies include serum lactate dehydrogenase (LDH) and beta-2 microglobulin (read with creatinine because it can normally be elevated in patients with elevated creatinine), which correlate with disease activity.
All patients diagnosed with CLL will not require treatment because CLL is a heterogeneous disease. Certain patients receiving no treatment have survival rates similar to that of a normal population; current treatment regimens cannot cure CLL except for allogeneic hematopoietic stem cell transplantation (HCT). Randomized control trials between immediate versus delayed treatments found no significant improvement in long-term survival with early treatment initiation.
According to the International Workshop on Chronic Lymphocytic Leukemia (iwCLL) criteria for "active disease," indications for treatment include:
Treatment of CLL is further classified into;
A. Patients without "active disease": This is further divided into early-stage asymptomatic CLL and localized SLL.
1. Early-stage asymptomatic CLL
2. Localized SLL
B. Patients with Active Disease
The main purpose of systemic therapy is for symptomatic relief, prolonged remission, and prolonged survival in patients. Symptomatic CLL is treated, and despite many recent advances, it remains an incurable disease. For those patients for whom treatment is considered, a pre-treatment assessment should be done, including gathering information about age and general health, other features such as TP53 abnormalities or adverse cytogenetics, relapsed disease, or treatment-naive status. The selection of initial therapy in patients with symptomatic/advanced CLL is based on the patient, patient preference, tumor characteristics, and therapy goals. Various treatment approaches for CLL use different combinations of the following agents. These agents significantly differ in their rates of time to progression, measurable residual disease (MRD), complete remission, and toxicities of drugs. There have been studies comparing different treatment modalities, and an individualized approach needs to be considered. Hence, patient preference plays a vital role in the ultimate treatment decision. Various drugs utilized in the management of CLL include;
Choice of Therapy: The preferred initial treatment choice is based upon genetic risk stratification of the tumor along with patient fitness assessment.
1. Genetic risk stratification is described as following:
2. Fitness Assessment: includes an assessment of comorbidities and the impact of these comorbidities on general function, liver function, and kidney function. Tools used for this assessment include the Eastern Cooperative Oncology Group performance status (ECOG PS), Cumulative illness rating scale (CIRS), geriatric assessment tools, and creatinine clearance to estimate renal function. Eligibility for targeted agents varies, depending upon the toxicity of the agent being used and the predicted tolerability based upon the patient's general fitness and comorbidities. Eligibility is more restrictive for chemoimmunotherapy. Patients are usually considered unfit for chemoimmunotherapy with intense regimens such as fludarabine, cyclophosphamide, and rituximab (FCR) if they have one or more of the following findings: ECOG PS of >/=2, CIRS >6, significant hepatic impairment (Child-Pugh class B or C), and creatinine clearance (CrCl) <70 mL/min.
a. Very high-risk disease: 17p deletion and/or TP53 mutations: These patients are at high risk of not responding to initial treatment with chemoimmunotherapy, or relapsing immediately after achieving remission. Initial treatment options include:
b. High-risk disease: IGHV unmutated (without 17p deletion and TP53 mutation): These patients do respond to initial treatment with chemoimmunotherapy; however, targeted agents are preferred due to an improvement in progression-free survival (PFS) and overall survival (OS) benefit compared to other chemoimmunotherapy. Treatment of choice is strongly based on patient preference and patient comorbidities. Initial treatment options include:
c. Standard-risk disease: IGHV mutated (without 17p deletion and TP53 mutation): In these patients, PFS and OS appear to be similar regardless of targeted therapy or chemoimmunotherapy being used in the patient. These patients are further categorized into Fit and Unfit based upon their Fitness assessment.
Fit Patients: Clinically fit patients with IGHV-mutated CLL and without 17p deletion or TP53 mutation may either choose targeted therapy or chemoimmunotherapy depending upon patient preference and Fitness assessment. Intensive Chemoimmunotherapy (FCR or BR) may be preferred by patients desiring a long treatment-free interval. Options include:
Unfit Patients: The management of patients with limited functional status is informed by the genetic features of the tumor (17p deletion, TP53 mutation, and IGHV mutation status). Many clinically unfit patients with comorbidities may benefit from treatment with single-agent ibrutinib, fixed duration venetoclax plus obinutuzumab, single-agent acalabrutinib, and/or the combination of bendamustine plus rituximab. Chlorambucil plus obinutuzumab is a treatment option for IGHV-mutated CLL in older patients with comorbidities.
Initial Treatment Options
1. Targeted Agents
Bruton tyrosine kinase (BTK) inhibitors
C. Management of complications of CLL and its therapy
CLL/SLL is characterized by hypo/agammaglobulinemia, which increases the risk of infections, especially Staphylococcus, H. influenza, Pneumococcus, and herpes. These infections can be managed with antimicrobials for bacterial, fungal, or viral infections. For refractory infections in patients with hypogammaglobinemia, or for 2 or more severe infections within a timeframe of 6-month, monthly IVIG infusions are considered.
CLL/SLL also produces autoantibodies directed against RBCs and platelets, leading to immune-mediated hemolytic anemia and thrombocytopenia. These can be acutely managed with packed RBC transfusion for anemia and platelet transfusion for bleeding secondary to thrombocytopenia. The cytopenias can be eventually treated with prednisone.
D. Relapsed/Refractory CLL
It is important to confirm relapsed/refractory CLL histologically prior to restarting treatment. Recurrent CLL in asymptomatic patients should be monitored for symptoms requiring treatment. Richter's transformation should specifically be excluded. The treatment of choice at relapse depends upon the initial treatment used and the initial duration of response to that treatment.
Ibrutinib is the first-line therapy to improve progression-free survival and response to treatment in relapsed/refractory CLL. Other drugs of choice for relapsed CLL include idelalisib (a phosphoinositide 3'-kinase [PI3K] delta inhibitor), Alemtuzumab (a monoclonal antibody directed against CD52, a cellular marker found in CLL) and venetoclax (Bcl-2 inhibitor). Venetoclax is actively used in refractory CLL patients with 17p deletion. Venetoclax induces brisk apoptosis and occasionally induces tumor lysis syndrome. Anti-CD19 chimeric antigen receptor (CAR) T-cell therapy has also been active in refractory cases. Anti-CD20 monoclonal antibody (rituximab, ofatumumab, obinutuzumab) may briefly alleviate symptoms in relapsed/refractory CLL patients.
Allogeneic Hematopoietic Stem Cell Transplantation is rarely performed in CLL but has been used in refractory cases in appropriate patients. Those with a very aggressive form of the disease, such as patients with 17p deletion, especially in younger patients, HLA-matched donors, should be recommended to get bone marrow transplant. Those without a matched donor or older in age can be given a trial of ibrutinib. Palliative radiation therapy can be given to chemotherapy-resistant areas of lymphadenopathy, liver, and spleen. Total body irradiation occasionally helps relieve symptoms temporarily.
Two staging systems are used in CLL patients. The modified Rai-Sawitsky staging in the United States and the Binet staging in Europe.
1. RAI Classification
2. Binet Classification
* Sites considered: Cervical, axillary, and inguinal lymph nodes; liver; and spleen.
In patients with CLL, the survival period could range from 2 to >20 years with a median survival of 10 years. The patients who present as Rai stage 0-II may survive for 5 to 20 years with no treatment. Lymphocyte doubling time is a prognostic factor of CLL, defined as the number of months it takes to double the absolute lymphocyte count. A more aggressive expression of CLL is seen in untreated patients with a lymphocyte doubling time of <12 months. Favorable prognostic factors include mutated Ig heavy chain variable region, 13 q deletion, low expression of ZAP-70, and low CD38 levels on flow cytometry. Unfavorable prognostic factors include specific high-risk cytogenetics abnormalities such as 17p deletion and 11q deletion. The patients with multiple chain lymphadenopathy, hepatosplenomegaly, anemia, and thrombocytopenia have a worse prognosis. One of the commonly used tools to predict CLL related outcomes includes CLL-IPI (International Prognostic Index for Chronic Lymphocytic Leukemia).
Complications accompanying CLL may include increased susceptibility to infections, particularly of the respiratory tract, progression to diffuse large B-cell lymphoma (Richter syndrome), an elevated risk of other malignancies (e.g., cancers of the skin, lungs, and GI tract), and immune system issues, where the immune system attacks red blood cells or platelets, although this is rare.
Patients will CLL need to understand the nature of their disease, the staging criteria, and where they stand within that staging, the treatments available, and their prognosis, given the precise nature of their disease. All treatment and management decisions should involve the patient and their family, and in late-stage disease, psychological and emotional support from qualified mental health professionals is in order.
CLL is a complex disorder best managed by an interprofessional team that includes an internist/general practitioner, hematologist/oncologist, hematopathologist, and radiologist.
Given that most patients with CLL are asymptomatic, treatment is not recommended for everyone. The recommendation for treatment depends on severe disease symptoms or rapidly progressing disease. Symptoms such as severe fatigue interfering with daily activities, B-symptoms, recurrent infections, or increased tumor burden indicate early treatment. Rapidly progressing disease such as an absolute lymphocyte count doubling time of fewer than 12 months is also an indication for early treatment.
For patients who are not considered for treatment, regular follow-up at 3-month intervals is recommended. If the patient has developed increasingly abnormal laboratory finds or is symptomatically worse, further care should be discussed with the oncologist. At the 12-month mark, depending on the symptoms and pace of disease, a decision on whether treatment is needed can be made.
Symptomatic CLL is treated, and despite many recent advances, it remains an incurable disease. However, the use of newer biological agents appears to be making some improvement in lifespan. For symptomatic patients, the outlook is dependent on various disease characteristics and underlying comorbidities, but those who are asymptomatic may have a normal life span. [Level 2]
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