Mammary epithelioid myofibroblastoma arising in bilateral gynecomastia: case report with immunohistochemical profile.

Myofibroblastoma of the breast is a rare benign neoplasm, which has rarely been reported in association with gynecomastia. We report a case of a 25-year-old male patient with an epithelioid myofibroblastoma arising in a context of bilateral gynecomastia. The lesion was composed of nests and cords of epithelioid cells, with round to oval nuclei, granular chromatin, and distinct nucleoli dispersed in a myxoid to collagenous stroma with marked vascular proliferation. Immunohistochemical profile showed diffuse positivity for vimentin and focal immunoreactivity for desmin, whereas cytokeratins (CAM5.2 and AE1/AE3), EMA, alpha smooth muscle actin, actin HHF35, CEA, S100, factor VIII, neuron-specific enolase, CD31, and CD34 were all negative. We emphasize that this diagnosis is difficult to establish, owing to the rarity of this variant and clinical presentation.