RESUMEN
A case of adenoid cystic carcinoma (ACC) of the breast in a 66-year-old woman is reported herein. ACC accounts for about 0.1% of all breast cancers. Our patient presented with a small, elastic and hard mass, measuring 2.0x2.0 cm, between both outer quadrants of the right breast. Although physical examination, ultrasonography and magnetic resonance (MR) mammography suggested a benign tumor, aspiration biopsy cytology (ABC) was performed twice, and the second ABC specimen was evaluated as suspicious for breast carcinoma. Breast conserving surgery with a level II lymph node dissection was subsequently performed. There was no lymph node metastases and estrogen receptor (ER) status was negative. Light microscopy revealed various growth patterns, with the cells showing biphasic cellularity. According to immunohistochemical analyses, CEA, actin and vimentin were positive, S-100 protein was negative, and the cytokeratin reaction was partially positive. Therefore, ACC of the breast was diagnosed. Although ACC of the breast is a rare neoplasm, it should be considered in the differential diagnosis even if various diagnostic imaging studies suggest a benign tumor of the breast. Awareness of this tumor will help prevent misdiagnosis.