Myoepithelioma breast: clinically masquerading as breast carcinoma.

Pure myoepithelioma of breast is an extremely rare tumor. Only a few cases have been reported in the literature so far. A 30-year old female presented with a large fungating mass arising from the areolar region of her right breast of six months duration. A clinical diagnosis of breast carcinoma was made and a mastectomy was performed. The specimen measured 23×22×9 cm with attached skin, and showed a large white ulcerated growth with areas of necrosis and hemorrhage. No normal breast tissue, nipple or areolar region was seen. Histopathological examination showed oval to spindle cells arranged in fascicles and bundles with whorling pattern in places showing mild pleomorphism with oval to spindle-shaped vesicular nuclei, prominent eosinophilic nucleoli, eosinophilic cytoplasm and clear cell changes in places, along with perivascular hyalinization and collagenization. Differential diagnosis of pleomorphic hyalinizing angiectatic tumor, solitary fibrous tumor, perivascular epithelioid cell tumor, mammary type myofibroblastic tumor and myoepithelioma were all considered. Immunohistochemistry for vimentin, smooth muscle actin, calponin, caldesmon, p63, epithelial membrane antigen, S-100, CD-31, CD-34, muscle specific antigen, myogenin, desmin, and pancytokeratin was carried out. On the basis of positive staining for vimentin, actin, p63 (nuclear), calponin and caldesmon (focal), a final diagnosis of myoepithelioma was considered; however, cytokeratin negativity was an unusual finding. This case was considered worthy of documentation because of its rarity, and because it highlights the importance of proper clinical examination and radiological examination to prevent misdiagnosis.