Malignant myoepithelioma of the breast: case report with review of literature.

Myoepithelial lesions of the breast are extremely rare and can present with a diverse morphology. We report a case of malignant myoepithelioma characterized by proliferation of atypical oval to polygonal cells expressing typical myoepithelial markers. A 45-year-old lady presented with a mass in the left breast. Fine needle aspiration yielded a cellular smear with large papillae-like clusters of monomorphic cells with naked nuclei in the background. A diagnosis of sub-areolar sclerosing duct hyperplasia was made on cytology and the patient underwent excision. The surgical specimen showed a grey-white 5x3 cm mass on cut surface. Histopathology revealed mitotically active (5-6 per 10hpf) oval to polygonal cells tumor cells with clear to eosinophilic cytoplasm arranged in the form of nodules separated by dense sclerotic stroma mimicking clear cell or adenoid-cystic carcinoma. A diagnosis of malignant myoepithelioma was made as the cells were CK14 and SMA positive, and negative for ER and PR on immunohistochemistry. We discuss the unusual morphological features of malignant myoepithelioma, cytological findings and the important differential diagnoses of malignant myoepthelial lesions. A high degree of suspicion with a keen eye for morphological details coupled with relevant immunohistochemistry will aid in arriving at the diagnosis.