Myeloid sarcoma of the breast in an aleukemic patient: a rare entity in an uncommon location.

Myeloid sarcoma (MS) is an extramedullary solid neoplasm of immature myeloid cells. These tumours usually develop in concurrence with or following acute leukemia. The breast is an uncommon site for presentation of this tumour, where it is often misdiagnosed as lymphoma or carcinoma.A 33- year-old female presented with a right breast lump in a private hospital, which was diagnosed as ductal carcinoma on lumpectomy. Subsequently she developed a lump in the left breast and a similar diagnosis of carcinoma was made on biopsy. A left mastectomy was performed. Histopathological examination revealed a tumour composed of mononuclear cells arranged in sheets and cords with round to oval vesicular nuclei and occasional prominent nucleoli. IHC for CK was very weak and focal. The tumour cells were immunonegative for ER, PR, Her2neu,epithelial membrane antigen, e-cadherin, CD3 and CD20. Diffuse immunopositivity for myeloperoxidase, CD34 and CD117 established a diagnosis of myeloid sarcoma. A histopathological review of the right breast lesion, with immunohistochemistry, also confirmed the diagnosis of myeloid sarcoma. Investigatory workup for acute myeloid leukemia, including bone marrow aspirate and biopsy and karyotypic studies, proved negative. The patient was treated with high dose cytarabine (HDAC) regimen and was disease free during the 12-month follow-up.Although extremely rare, awareness of such a presentation is crucial. This case also illustrates that careful histopathological review along with an expanded panel of immunohistochemistry is extremely important for recognizing such cases as a misdiagnosis can lead to unnecessary surgery and inappropriate therapy.