A bone marrow aspirate from a 40-year-old man shows 35% blasts. Immunophenotyping is pending. Which single finding on the aspirate would establish that the blasts are of myeloid rather than lymphoid lineage?

• A Myeloperoxidase positivity in blast granules ✓
• B Coarse PAS block positivity
• C Strong focal acid phosphatase positivity
• D Nuclear TdT positivity

Explanation

Myeloperoxidase is present in primary granules of myeloid precursors and its positivity in blasts confirms AML; Sudan black B parallels it. Coarse PAS blocks favor ALL (or erythroid precursors in M6), focal strong acid phosphatase is a feature of T-ALL, and TdT marks primitive lymphoid blasts. Among these four, only MPO is specific for the myeloid series.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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