Myeloid-lineage blasts with histiocytoid differentiation in TP53 mutated acute myeloid leukemia: a deceptive morphologic overlap with mature malignant histiocytic neoplasms.

Here, we report a case of TP53-mutated acute myeloid leukemia (AML) with monocytic differentiation that showed striking histiocytoid morphologic transformation following induction chemotherapy. Post-treatment blasts demonstrated significant morphologic overlap with mature malignant histiocytic neoplasms, particularly histiocytic sarcoma subtype, creating a potential diagnostic pitfall. Retained myeloperoxidase expression, together with the absence of cyclin D1 expression, supported a diagnosis of persistent AML rather than divergent histiocytic differentiation.