A 52-year-old man presents with progressive fatigue, early satiety, and left upper quadrant heaviness. Examination reveals massive splenomegaly extending to the umbilicus; no lymphadenopathy. CBC: Hb 9.8 g/dL, WBC 3,200/µL, platelets 110,000/µL. Peripheral smear shows characteristic cells with hairy cytoplasmic projections. TRAP (tartrate-resistant acid phosphatase) stain is positive. Which marker pattern on flow cytometry confirms the diagnosis?
- A CD5+, CD10+, CD23-
- B CD13+, CD33+, MPO+
- C CD19+, CD20+, CD5-, CD103+, CD123+ ✓
- D CD10+, CD19+, BCL6+
Correct answer: C. CD19+, CD20+, CD5-, CD103+, CD123+
Explanation
Hairy cell leukemia classically presents with pancytopenia, massive splenomegaly, and characteristic hairy cells that are TRAP-positive. Flow cytometry is positive for bright CD20, CD11c, CD25, CD103, and CD123, and negative for CD5 and CD23. CD5+/CD23- is CLL/SLL; CD10+/BCL6+ is follicular lymphoma or DLBCL; CD13/CD33/MPO positivity indicates myeloid lineage (AML).
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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