[Microgranular-type acute promyelocytic leukemia with weak myeloperoxidase staining: difficulty of morphological diagnosis].

The 2017 World Health Organization (WHO) classification states that acute promyelocytic leukemia (APL) always presents with strong myeloperoxidase staining. However, we herein report of a 40-year-old woman with the microgranular variant of acute promyelocytic leukemia presenting with weak myeloperoxidase (MPO) staining. The leukemic cells were morphologically similar to monocytic cells, showing distorted-shaped nuclei and weak MPO staining. However, flow cytometry revealed positivity of CD2, CD34, and human leucocyte antigen-DR (HLA-DR) and pointed toward a diagnosis of APL. PML-RARA mRNA detection finally led the patient to a definitive diagnosis. The patient achieved complete remission by induction chemotherapy including tretinoin, cytarabine and idarubicin, and no differentiation syndrome was observed.