A 42-year-old woman presents with fatigue and gingival bleeding. Bone marrow examination shows a proliferation of myeloblasts and monoblasts together with numerous eosinophils containing large basophilic granules and vacuolated cytoplasm. Cytogenetics show inversion of chromosome 16. Which fusion transcript is expected?

• A KMT2A-AFF1
• B PML-RARA
• C RUNX1-RUNX1T1
• D CBFB-MYH11 ✓

Explanation

inv(16)(p13.1q22) fuses CBFB to MYH11, encoding a smooth muscle myosin heavy chain, and defines AML with inv(16), formerly FAB M4 eosinophilia. The morphologic clue is abnormal marrow eosinophils with coarse basophilic granules. PML-RARA corresponds to t(15;17), RUNX1-RUNX1T1 to t(8;21), and KMT2D-AFF1 to t(4;11); none of these produce dysplastic eosinophils. Both core binding factor leukemias carry an intermediate to favorable prognosis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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