INFILTRATING MYOEPITHELIOMA OF THE BREAST

Tumors exclusively composed of myoepithelial cells are extremely uncom mon in the breast. We report such a tumor in a 25-year-old white woman . Clinical and ultrasonographic findings suggested a small benign lesi on of the breast. Nodulectomy performed for intraoperative diagnosis f ound a malignant spindle cell tumor. Consequently, a quadrantectomy wi th axillary lymphadenectomy was carried out. Routine stains suggested a tumor of myoepithelial origin that infiltrated the fat tissue; immun ocytochemical stains demonstrated strong cytoplasmic reactivity for ac tin, cytokeratin, S-100 protein, and vimentin. Glial fibrillary acidic protein (GFAP) was detectable only in scattered tumor cells. Examinat ion of the resected breast tissue and lymph nodes did not reveal addit ional tumor foci. Due to the evidence of infiltrative growth in this c ase and to the uncertain prognosis for breast myoepitheliomas, we supp ort the previously proposed term ''infiltrating myoepithelioma'' for t his rare tumor. We also suggest that immunocytochemistry should be man datory in every spindle cell tumor of the breast because this morpholo gical pattern is shared by several tumors with different biological be haviors.