Epithelioid cell myofibroblastoma of the breast: a potential diagnostic pitfall

A 40-year-old woman presented with a 0.9-cm, non- calcified, well-circumscribed nodular mass in her upper outer left breast, detected on screening mammo- gram. Ultrasound examination confirmed the presence of a solid hypoechoic nodule. Lumpec-tomy was performed. The surgical specimen was com- prised of breast parenchyma measuring 2.5 cm in greatest dimension. The cut section revealed a 1-cm, well-circumscribed nodule, whitish in color and firm in appearance. Histologic examination revealed a homogeneously highly cellular tumor composed of medium-to-large sized epithelioid cells with abundant eosinophilic cytoplasm and round to oval, centrally or eccentrically placed nuclei with one or two prominent nucleoli. Bi-nucleated or multi-nucleated neo-plastic cells, closely reminiscent of Reed-Sternberg-like cells, were focally seen. Thin-to-thick eosino-philic collagen bands were interspersed among neo-plastic cells. Immunohistochemically neoplastic cells were diffusely stained with desmin and only focally to alpha-smooth muscle actin and CD34.The morphologic and immuno-histochemical features of the present case are consistent with the diagnosis of ‘‘epitheliod cell myofi- broblastoma (MFB)’’. This is a very rare variant of MFB that may represent a diagnostic challenge due to the alarming features exhibited by neoplastic cells.