Chronic Lymphocytic Leukemia is the Most Common Type of Leukemia in Older Adults
Chronic lymphocytic leukemia (CLL) is definitively the most common type of leukemia in older adults, representing 25% of all adult leukemias with a median age at diagnosis of 72 years. 1
Epidemiology and Incidence
- CLL has an incidence of 4.2/100,000/year in the Western world 1
- The incidence increases dramatically with age:
- CLL represents the most frequent leukemia of adults (25%) 1
Distinguishing Features of CLL
CLL is characterized by:
- Sustained increase of peripheral CD5+ B-lymphocytes (≥5 × 10^9/L) for at least 3 months 1
- Characteristic immunophenotype: CD5+, CD19+, CD20+ (low), CD23+, surface immunoglobulin (sIg) low, CD79b low 1, 2
- Morphologically mature lymphocytes with narrow cytoplasm border and dense nucleus lacking discernible nucleoli 1
Comparison to Other Lymphocytic Leukemias
- Chronic lymphocytic leukemia (CLL) is significantly more common than:
- Acute lymphocytic leukemia (ALL) - which is more common in children
- Chronic myelogenous leukemia (CML) - which accounts for a smaller percentage of adult leukemias
- "Late onset lymphocytic leukemia" is not a recognized clinical entity in standard classification systems
Diagnostic Criteria
The diagnosis of CLL requires:
- ≥5000 B lymphocytes/µL in peripheral blood for at least 3 months 1
- Confirmation of clonality by flow cytometry 1
- Characteristic immunophenotype (CD5+, CD19+, CD20+ low, CD23+) 2
Clinical Relevance
Understanding that CLL is the most common leukemia in older adults has important implications:
- Treatment approaches must consider the advanced age and comorbidities of most patients 3
- Traditional chemotherapy regimens may be difficult for older patients to tolerate 3
- Newer targeted therapies (BTK inhibitors, BCL2 inhibitors) have improved outcomes in elderly CLL patients 4
- The watch-and-wait strategy is appropriate for early-stage asymptomatic disease 2
Prognostic Factors
Several factors influence prognosis in CLL:
- Cytogenetic abnormalities, particularly del(17p) and del(11q) 2
- IGHV mutational status 2
- Expression of CD38 and ZAP70 2
CLL remains incurable with current therapies, but modern treatment approaches have significantly improved outcomes, even in elderly patients who constitute the majority of cases.