A unique clinical presentation of de novo acute promyelocytic leukemia as a myeloid sarcoma of the breast.

Myeloid sarcoma is a rare presentation of acute leukemia as a solid tumor at various extramedullary sites. It may present concurrently, before or after the onset of systemic bone marrow leukemia. Unusual clinical localization may lead to misdiagnosis, or delayed diagnosis and treatment. We describe the first case, to our knowledge, of de novo myeloid sarcoma of the breast confirmed as acute promyelocytic leukemia. Immunohistochemical analysis, flow cytometry, fluorescent in situ hybridization analysis and molecular analysis using RQ-PCR of tissue samples should be routine in determining the correct diagnosis in this setting.