INFILTRATING MYOEPITHELIOMA OF THE BREAST

Tumors exclusively composed of myoepithelial cells are extremely uncommon in the breast. We report such a tumor in a 25-year-old white woman. Clinical and ultrasonographic findings suggested a small benign lesion of the breast. Nodulectomy performed for intraoperative diagnosis found a malignant spindle cell tumor. Consequently, a quadrantectomy with axillary lymphadenectomy was carried out. Routine stains suggested a tumor of myoepithelial origin that infiltrated the fat tissue; immunocytochemical stains demonstrated strong cytoplasmic reactivity for actin, cytokeratin, S-100 protein, and vimentin. Glial fibrillary acidic protein (GFAP) was detectable only in scattered tumor cells. Examination of the resected breast tissue and lymph nodes did not reveal additional tumor foci. Due to the evidence of infiltrative growth in this case and to the uncertain prognosis for breast myoepitheliomas, we support the previously proposed term ''infiltrating myoepithelioma'' for this rare tumor. We also suggest that immunocytochemistry should be mandatory in every spindle cell tumor of the breast because this morphological pattern is shared by several tumors with different biological behaviors