A 55-year-old presents with splenomegaly, peripheral blood showing small lymphocytes with 'hairy' cytoplasmic projections, and TRAP (tartrate-resistant acid phosphatase) positivity on cytochemistry. Which signaling pathway mutation is found in virtually all cases of this entity?
- A JAK2 V617F
- B NPM1 insertion
- C BRAF V600E ✓
- D FLT3-ITD
Correct answer: C. BRAF V600E
Explanation
Hairy cell leukemia (HCL) is characterized by BRAF V600E mutation in virtually 100% of cases, making it both pathognomonic and therapeutically targetable with BRAF inhibitors (vemurafenib). The cells express CD11c, CD25, CD103, CD123, and annexin A1, and show TRAP positivity. JAK2 V617F is the hallmark of polycythemia vera and essential thrombocythemia, while FLT3-ITD and NPM1 are AML markers.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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