What is the most common type of leukemia in adults?

Chronic Lymphocytic Leukemia is the Most Common Adult Leukemia

Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in adults, representing approximately 25% of all adult leukemias in the western world. 1, 2 This hematologic malignancy has distinctive epidemiological patterns and clinical characteristics that make it a significant concern in adult medicine.

Epidemiology of CLL

• Incidence rate of 4:100,000/year in the general population 2
• Dramatically increases with age to >30:100,000/year in individuals over 80 years 1
• Median age at diagnosis is 69-72 years 2, 3
• Only 10-14% of CLL patients are diagnosed before age 55 2, 1
• Higher prevalence in males than females 4
• More common in white populations than in black populations 4
• Highest incidence rates reported in Australia, USA, Ireland, and Italy 4

Diagnostic Criteria

CLL diagnosis requires:

• Sustained peripheral blood lymphocytosis ≥5 × 10^9/L for at least 3 months 2, 1
• Characteristic immunophenotype showing:
  • CD5+ (T-cell antigen expressed on leukemic B-cells)
  • CD19+, CD20+ (dim expression), CD23+
  • Low surface immunoglobulin expression
  • Restricted kappa or lambda light chain expression 2, 1
• Blood smear showing predominance of small, mature-appearing lymphocytes 2

Staging and Prognosis

Two major staging systems are used:

1. Binet Staging System (more common in Europe):

   • Stage A: <3 lymphoid areas involved, Hb ≥10 g/dL, platelets ≥100×10^9/L
   • Stage B: ≥3 lymphoid areas involved, Hb ≥10 g/dL, platelets ≥100×10^9/L
   • Stage C: Hb <10 g/dL and/or platelets <100×10^9/L 1

2. Rai Staging System:

   • Stage 0: Lymphocytosis only
   • Stage I: Lymphocytosis + lymphadenopathy
   • Stage II: Lymphocytosis + hepatomegaly/splenomegaly
   • Stage III: Lymphocytosis + anemia
   • Stage IV: Lymphocytosis + thrombocytopenia 1

Treatment Approach

• Early-stage asymptomatic disease: "Watch and wait" strategy with monitoring every 3 months 2, 1

• Treatment indications:

  • Significant B symptoms (fever, night sweats, weight loss)
  • Progressive lymphadenopathy or organomegaly
  • Progressive lymphocytosis with doubling time <6 months
  • Cytopenias not caused by autoimmune phenomena
  • Advanced disease (Binet stage C or Rai stages III-IV) 1

• Modern treatment options:

  • BTK inhibitors (ibrutinib and newer agents)
  • BCL2 inhibitors (venetoclax)
  • Anti-CD20 antibodies in combination therapy
  • PI3K inhibitors 5, 3, 6

Clinical Pearls and Pitfalls

• CLL and small lymphocytic lymphoma (SLL) are considered the same disease with different presentations 3
• Genetic testing (FISH for del(17p), TP53 mutations, IGHV mutation status) is crucial for treatment selection 1, 3
• Avoid premature treatment of asymptomatic early-stage disease as there is no survival benefit 1
• Distinguish between disease-related and autoimmune cytopenias, as management differs significantly 1
• Fixed-duration therapies with targeted agents are gaining prominence as they are cost-effective and offer treatment-free intervals 1, 6
• The 5-year survival rate is 83% for patients <65 years and 68% for those ≥65 years 4

CLL management has undergone a paradigm shift from chemotherapy-based regimens to targeted therapies with improved outcomes and tolerability, particularly important for the predominantly older patient population affected by this disease 5, 7.