ZMYND11::MBTD1 Fusion in Myeloid/NK Cell Precursor Leukemia: A Case Report With Literature Review and Diagnostic Implications.

Myeloid/NK cell precursor leukemia (MNKPL) is a rare, aggressive entity often misdiagnosed as acute myeloid leukemia (AML) or aggressive NK cell leukemia (ANKL) because of overlapping markers (CD7+, CD13/CD33+, CD56+, myeloperoxidase [MPO]-). We report a patient initially diagnosed with ANKL; subsequent flow-cytometric reevaluation (CD7+, CD13+, CD33+, CD34+, CD56+, CD117+, MPO-) supported a diagnosis of MNKPL. RNA sequencing and nested PCR identified an in-frame ZMYND11::MBTD1 fusion. A review of published ZMYND11::MBTD1 leukemias (n = 5) found immunophenotypes highly consistent with MNKPL, suggesting prior misclassification. These findings support ZMYND11::MBTD1 as a recurrent lesion in MNKPL and a practical aid to diagnosis and treatment selection.