Primary extramedullary myeloid tumor of the breast: a case report and review of the literature.

Primary extramedullary myeloid tumors (PEMMT) are extramedullary proliferations of myeloid cells occurring in the absence of an antecedent myeloproliferative disorder. They have predilection for the skin, lymph nodes, central nervous system, and small intestine. Breast is an uncommon location for PEMMT and only a few cases have been reported so far in the medical literature. Many of these cases have been initially misdiagnosed. We reviewed all the reported cases of PEMMT of the breast in the English-language literature since 1965. In addition, we present a new case of PEMMT of the breast who presented with a mass in her right breast mimicking a breast malignancy and was initially misdiagnosed as non-Hodgkin's lymphoma. A careful histologic examination with immunohistochemical studies revealed the presence of PEMMT of the breast. Treatment with systemic chemotherapy and local radiotherapy rendered a complete remission. Seventeen cases of PEMMT of the breast were reported in the English literature from 1965 to 2003. Most of the cases were misdiagnosed initially as lymphomas, breast carcinomas, or malignant melanomas. PEMMT of the breast is a poorly recognized entity whose diagnosis frequently challenges both the pathologist and the oncologist. Given the small number of patients reported no optimal treatment has been defined, but systemic chemotherapy similar to that given for acute myeloid leukemia with or without local radiotherapy may result in long remissions and avoid the progression to overt acute myeloid leukemia.