Which type of leukemia is the most common in adults?

• A. Acute myeloid leukemia (AML)
• B. Chronic lymphocytic leukemia (CLL)
• C. Acute lymphoblastic leukemia (ALL)
• D. Hairy cell leukemia

Answer: (B)

Chronic lymphocytic leukemia is the most common leukemia diagnosed in adults, especially in older individuals. It arises from malignant transformation of mature B lymphocytes, which accumulate in the blood, bone marrow, and lymphoid tissues. Many cases are found incidentally because patients may be asymptomatic for years. The typical picture includes persistent lymphocytosis and a B-cell immunophenotype commonly expressing CD5, CD19, and CD23. Clinically, patients may have painless lymphadenopathy, splenomegaly, fatigue, and infections due to impaired antibody production, with possible anemia or thrombocytopenia from marrow involvement. In contrast, acute leukemias like AML present acutely with marrow failure and are the most common acute leukemia in adults, ALL is most common in children, and hairy cell leukemia is a rare rare form. Thus, the most common adult leukemia is CLL.