Auer rod-like inclusions in marginal zone lymphoma: a potential diagnostic pitfall.

A 47-year-old man presented with leukocytosis and absolute lymphocytosis. Peripheral blood smear examination revealed atypical lymphoid cells containing striking Auer rod-like cytoplasmic inclusions, creating a strong morphologic impression of acute promyelocytic leukemia. However, flow cytometry demonstrated a mature monoclonal B cell population lacking myeloid differentiation, and bone marrow biopsy established the diagnosis of marginal zone lymphoma. This rare case highlights a major diagnostic pitfall and underscores that Auer rod-like inclusions are not exclusively restricted to myeloid neoplasms.