Chronic Lymphocytic Leukemia: Diagnosis and Prognostic Markers

Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in adults, and the incidence increases with increasing age.^1-3 The disease begins with the development of abnormal lymphocytes in the bone marrow. Because the leukemic cells multiply slowly at first, most people are asymptomatic for a few years. However, the leukemic cells eventually spread to other parts of the body, including the lymph nodes, liver, and spleen. The course of disease for CLL is variable and can be indolent, with slow progression that may not require treatment, or very aggressive.

This article discusses CLL and related diseases, including CLL symptoms, diagnosis, prognostic markers, staging, and treatment.

CLL epidemiology

CLL has an overall incidence of about 4.2 cases per 100,000 persons per year, and the median age at diagnosis is 72 years.³ The incidence is substantially higher in people older than 80 (30 cases per 100,000 persons per year), and only about 10% of CLL cases are in persons younger than 55.³ Family members of a patient with CLL have a 6- to 9-fold increased risk of developing the disease (see Sidebar for risk factors).^4-6

Pathophysiology: CLL and other leukemias

Leukemias develop because of alterations in the DNA of myeloid or lymphoid cells, but the process of development of malignant changes is not clear.

CLL is a lymphoproliferative disorder (a blood cancer) characterized by dysfunctional monoclonal B lymphocytes.^1,2 Small lymphocytic lymphoma (SLL) is considered the same disease, differing only in the sites of involvement. Whereas malignant B lymphocytes are primarily located in the lymph nodes and lymphoid tissue (such as the spleen and the tonsils) in SLL, they are present primarily in the bloodstream in CLL.⁷ This type of leukemia is classified “chronic” rather than “acute”, because of the slow speed at which abnormal leukocytes proliferate, and “lymphocytic” rather than “myelogenous”, based on the cell lineage (ie, lymphocyte vs myelocyte).⁴

The 3 other major subtypes of leukemia are

• Acute myelogenous leukemia (AML), the most common acute leukemia in adults. AML is an aggressive disease with a prognosis that varies with molecular subtype.
• Acute lymphoblastic leukemia (ALL), which accounts for about 80% of leukemia in children.
• Chronic myelogenous leukemia (CML), which is commonly due to a reciprocal translocation and fusion of BCR on chromosome 22 and ABL1 on chromosome 9.⁴

Symptoms of CLL

Many persons with CLL are asymptomatic in the early stages of the disease.^3,4 As the disease progresses, nonspecific symptoms develop and include⁴

• Enlarged, painless lymph nodes
• Fatigue
• Fever
• Pain in the upper left portion of the abdomen, primarily due to an enlarged spleen
• Night sweats
• Weight loss

Patients with CLL will typically develop frequent infections because an excess of leukemic cells reduces the number of functional leukocytes.^2,3 Some patients may develop autoimmune hemolytic anemia or autoimmune thrombocytopenia because of alterations of the immune system.^2,3

Diagnosis

Routine screening for CLL is not included in any current recommendations.^3,5 In many persons, diagnosis of CLL is made when abnormal leukocytosis is seen on a routine complete blood count (CBC).⁴  Laboratory diagnosis of  CLL is based on (1) the presence of ≥5×10⁹/L monoclonal B lymphocytes in the peripheral blood, and (2) circulating B lymphocyte clonality confirmed by flow cytometry.³ Peripheral blood smears should be examined by a hematopathologist who can identify leukemic cells characteristic of CLL.⁵ A bone marrow biopsy is typically only required when immunotyping of peripheral blood (flow cytometry of leukocyte subsets) is inconclusive.³

CLL prognostic markers

The prognosis for patients with CLL depends on many factors, including prognostic markers. Several prognostic markers are used to predict survival and guide treatment.^3,5 Common prognostic markers include

• Immunoglobulin heavy-chain variable gene segment (IGVH) mutation status: The unmutated form of this gene is associated with poor prognosis and significantly decreased survival compared with mutated IGHV, irrespective of the stage of the disease.⁵ The unmutated gene is also associated with a worse response to the chemoimmunotherapy regimen fludarabine-cyclophosphamide-rituximab.⁵ The mechanism(s) underlying the association between IGHV status and CLL prognosis not known.⁹
• Cell surface markers: Positivity for CD38, CD49d, or ZAP-70 is associated with shorter treatment-free survival, progression-free survival, and/or overall survival.⁵
• TP53 aberrations: del(17p) (deletion of the chromosome 17 [p] arm) or TP53 gene mutations affect tumor protein p53. If fluorescence in situ hybridization (FISH) indicates the absence of del(17p), TP53 sequencing should be performed. These aberrations are associated with a very poor prognosis (median overall survival of 24 to 60 months when treated with immunochemotherapy).³
• del(11q) (deletion of the long [q] arm of chromosome 11): del(11q) is associated with extensive lymphadenopathy, disease progression, and a short median survival (79 months).⁵
• del(13q) (deletion of the long [q] arm of chromosome 13: del(13q) is associated with a more favorable prognosis (longest median survival [133 months]).⁵
• Trisomy 12: About 16% of patients with untreated CLL have trisomy 12 (detected by FISH). If they have no other genetic lesions, these patients are at relatively low risk of disease progression and have a 10-year survival rate of 57%.⁵
• Complex karyotype: A high complex karyotype (≥5 unrelated chromosomal abnormalities) is an adverse prognostic factor independent of clinical stage, IGHV mutation status, and TP53 aberrations (because some chromosomal anomalies may be missed by FISH, a complex karyotype can be determined by using CpG oligonucleotides to stimulate cultured CLL cells into the metaphase stage of cell division, in which anomalies are more readily detectable).⁵
• High serum beta-2 microglobulin: Elevated levels of beta-2 microglobulin, a protein tumor marker, are an independent predictor of poor response to treatment, shorter treatment-free interval, and shorter overall survival.⁵ Levels, however, are influenced by CLL-dependent renal dysfunction.⁵

Prognostic indexes (eg, International Prognostic Index) have also been developed that incorporate various markers.^5,8

Staging and treatment

Two staging systems are used to determine disease stage in patients with CLL, both of which include factors such as hemoglobin level, platelet count, and lymphocytosis/lymphadenopathy.³ The Binet system categorizes patients as clinical stage A, B, and C, whereas the Rai system categorizes patients into stage 0 to IV.³ With both systems, higher stage indicates worse disease.³ Because most cases of CLL are “incurable,” treatment goals are to prolong survival and maintain or improve quality of life.³

Patients with early disease

Persons who have early-stage CLL and are asymptomatic (Binet stage A and B without active disease; Rai 0, I, and II without active disease) are typically followed with regular monitoring of symptoms and laboratory testing.^3,5 Treatment begins if there are signs of disease progression, such as development of chromosomal abnormalities or changes in blood cell counts (eg, hemoglobin, white blood cells, platelets), bone marrow or lymph node morphology, or serum markers (eg, high serum beta-2 microglobulin).^3,5

Patients with advanced disease

Treatment is recommended for persons with advanced disease (Binet stage A or B with active disease or stage C; Rai 0-II with active disease or Rai III-IV).3,5 Active disease is defined by the presence of at least 1 of the following³:

• Progressive bone marrow failure (development or worsening of anemia/thrombocytopenia)
• Massive, progressive, or symptomatic splenomegaly
• Massive, progressive, or symptomatic lymphadenopathy
• Progressive lymphocytosis
• Autoimmune complications (eg, thrombocytopenia not responsive to corticosteroids)
• Extranodal involvement (eg, kidney, lung)
• Disease-related symptoms, such as ≥10% weight loss in the past 6 months

Patients with CCL may be initially tested for IGHV and TP53 gene mutation status, del(17p), del(11q), serum beta-2 microglobulin levels, and cell surface markers CD38, CD49d, and ZAP-70. All can influence treatment choices, which include tyrosine kinase inhibitors, B-cell receptor inhibitors, and immune checkpoint inhibitors.^3,5,8,9 Treatment selection also takes into account factors such as other cytogenetic abnormalities, the patient’s physical status, medications, comorbidities, and treatment adherence.^3,5

Risk factors for CLL

Risk factors for development of CLL include⁴

• Older age
• Race: White individuals are more likely to develop CLL than are other races
• Family history of a blood or bone marrow cancer
• Exposure to certain chemicals (some herbicides, insecticides, and Agent Orange)
• Monoclonal B-cell lymphocytosis (see below)^5,6

Monoclonal B-cell lymphocytosis

Monoclonal B-cell lymphocytosis (MBL) occurs when abnormal B cells are present that have an immunophenotype of CLL, or related low-grade lymphoproliferative disorder, but the diagnostic criteria for CLL are not met. The condition is defined as⁵

• An absolute monoclonal B lymphocyte count of <5×10⁹/L that remains unchanged over 3 months
• Absence of palpable lymphadenopathy
• Other features seen in a lymphoproliferative disorder (eg, anemia, thrombocytopenia)

MBL has characteristics associated with a good prognosis, including IGHV mutations, a low frequency of TP53 mutations, and a relatively slower lymphocyte doubling time. MBL can be characterized based on flowcytometry findings as CLL-type MBL (75% of cases), atypical-CLL-type MBL, or non-CLL-type MBL (25% of cases).⁶ For all 3 categories, the frequency of progression to CLL is very low. Observation through yearly examinations and laboratory studies for CLL characteristics (eg, beta-2 microglobulin level, TP53 mutation status) is recommended.^5,6

How the laboratory can help

Quest Diagnostics offers testing for the diagnosis of CLL and for the management and follow-up of patients with CLL. Available testing includes routine laboratory studies as well as advanced testing, such as cytogenetics (eg, karyotyping, FISH), flow cytometry, mutation analysis, and immunophenotyping. Board-certified hematopathologists are available to examine blood smear and biopsy specimens.

Additional information is available at

• QuestDiagnostics.com/Healthcare-Professionals/About-Our-Tests/Cancer/Leukemia-Lymphoma
• QuestDiagnostics.com/Healthcare-Professionals/Clinical-Education-Center/FAQ/FAQ41

References

1. About chronic lymphocytic leukemia. American Cancer Society. Revised January 12, 2021. Accessed July 18, 2022. https://www.cancer.org/content/dam/CRC/PDF/Public/8679.00.pdf

2. Chronic lymphocytic leukemia treatment (PDQ^®)-health professional version. National Cancer Institute. Updated February 25, 2022. Accessed July 18, 2022. https://www.cancer.gov/types/leukemia/hp/cll-treatment-pdq

3. Eichhorst B, Robak T, Montserrat E, et al. Chronic lymphocytic leukaemia: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2021 Jan;32(1):23-33. doi: 10.1016/j.annonc.2020.09.019

4. Chennamadhavuni A, Lyengar V, Shimanovsky A. Leukemia. In: StatPearls [Internet].  StatPearls Publishing; 2022. https://www.ncbi.nlm.nih.gov/books/NBK560490/

5. National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines^®). Chronic lymphocytic leukemia/small lymphocytic lymphoma. Version 3.2022. Published June 3, 2022. https://www.nccn.org/

6. Maitre E, Troussard X. Monoclonal B-cell lymphocytosis. Best Pract Res Clin Haematol. 2019;32(3):229-238. doi:10.1016/j.beha.2019.06.002

7. Yoshino T, Tanaka T, Sato Y. Differential diagnosis of chronic lymphocytic leukemia/small lymphocytic lymphoma and other indolent lymphomas, including mantle cell lymphoma. J Clin Exp Hematop. 2020;60(4):124-129. doi:10.3960/jslrt.19041

8. Parikh SA, Rabe KG, Kay NE, et al. The CLL International Prognostic Index predicts outcomes in monoclonal B-cell lymphocytosis and Rai 0 CLL. Blood. 2021;138(2):149-159. doi:10.1182/blood.2020009813

9. Lee J, Wang YL. Prognostic and predictive molecular biomarkers in chronic lymphocytic leukemia. J Mol Diagn. 2020;22(9):1114-1125. doi:10.1016/j.jmoldx.2020.06.004

Models used for illustrative purposes

Published date: Sep 2022