Chronic Lymphocytic Leukemia
Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in Western populations and is a clonal proliferation of mature-appearing B lymphocytes that accumulate in the blood, bone marrow, and lymphoid tissues. It is biologically the same entity as small lymphocytic lymphoma, differing mainly in whether the disease presents predominantly in the blood or in lymph nodes. Its course ranges from indolent to progressive.
Definition
Chronic lymphocytic leukemia is a clonal neoplasm of mature CD5-positive B lymphocytes that accumulate in the peripheral blood, bone marrow, and lymphoid organs, diagnosed by a sustained monoclonal B-lymphocytosis with a characteristic immunophenotype, and biologically identical to small lymphocytic lymphoma.
Scope
This topic covers the nature of CLL as a mature B-cell neoplasm: its characteristic immunophenotype, the diagnostic lymphocyte threshold, the prognostic role of genetic and molecular markers, and its relationship to small lymphocytic lymphoma. It is reference material on the disease and its appraisal, not a treatment guide; specific therapies and dosing are out of scope.
Key concepts
- Mature clonal B lymphocytes
- Characteristic CLL immunophenotype (CD5, CD19, CD23)
- Monoclonal B-cell lymphocytosis as a precursor state
- CLL and small lymphocytic lymphoma as one entity
- IGHV mutation status
- TP53 and del(17p) as adverse markers
- B-cell receptor signaling
Mechanisms
CLL arises from a clonal population of mature B lymphocytes whose survival is supported by B-cell receptor signaling and by interactions with the tissue microenvironment, leading to gradual accumulation rather than rapid proliferation. The clone displays a characteristic surface immunophenotype that distinguishes it from other lymphoproliferative disorders. Biological behavior is strongly shaped by molecular features, notably the mutation status of the immunoglobulin heavy-chain variable (IGHV) genes and the presence of TP53 abnormalities, which carry prognostic weight (Chiorazzi et al., 2005; Hallek et al., 2018).
Clinical relevance
CLL illustrates how a leukemia can be defined by a distinctive immunophenotype and stratified by molecular markers, and it is frequently encountered in hematology practice and literature. This entry describes the disease and its biology at a reference level and is not a basis for individual diagnostic or treatment decisions.
Epidemiology
CLL is predominantly a disease of older adults, is more common in men, and is the most frequent leukemia among adults in Western countries; it is notably less common in some East Asian populations (Chiorazzi et al., 2005).
Evidence & guidelines
Diagnosis and response assessment for CLL are standardized by the International Workshop on CLL (iwCLL) guidelines, including the diagnostic monoclonal B-lymphocytosis threshold and immunophenotypic criteria, while classification within lymphoid neoplasms follows the WHO 5th edition (Hallek et al., 2018; Alaggio et al., 2022).
History
CLL was long recognized clinically as an indolent lymphocytic leukemia, and staging systems introduced in the 1970s and 1980s organized its prognosis. Subsequent decades reframed it as a mature B-cell neoplasm identical to small lymphocytic lymphoma and added molecular markers such as IGHV mutation status and TP53 abnormalities to its assessment (Chiorazzi et al., 2005; Hallek et al., 2018).
Key figures
- Kanti Rai
- Michael Hallek
- Nicholas Chiorazzi
Related topics
Seminal works
- chiorazzi-2005
- hallek-2018
Frequently asked questions
- Is CLL the same disease as small lymphocytic lymphoma?
- Yes. CLL and small lymphocytic lymphoma are considered the same neoplasm of mature clonal B cells; the labels reflect whether the disease is manifested mainly in the blood and marrow (CLL) or predominantly in lymph nodes (SLL).
- Why do IGHV mutation status and TP53 matter in CLL?
- They are major prognostic markers: IGHV-mutated and IGHV-unmutated CLL behave differently, and TP53 abnormalities (including del(17p)) are associated with a more adverse course, so they inform how the disease is appraised.