Mammary Myofibroblastoma with Unusual Morphological and Immunohistochemical Features.

Mammary myofibroblastoma (MFB) is a rare mesenchymal tumor, derived from mammary stromal fibro/myofibroblasts, which has various morphological features and characteristic immunohistochemical staining. The epithelioid morphologic variant is defined, accordingly, as a proliferation of exclusively or predominantly (>50%) epithelioid cells, variably embedded in a myxoid to fibrous stroma. These histological and cytological features may pose a diagnostic challenge mainly with metaplastic carcinoma and invasive lobular carcinoma of the breast.