Case report of microcystic adnexal carcinoma primary of breast skin

Background : We report a case of extremely rare microcystic adnexal carcinoma originating adnexally and tentatively diagnosed based on cytological findings as adenocarcinoma of mammary gland origin. Case : A 86-year-old woman found to have a 2 cm tumor in the C region of the left breast, and undergoing breast aspiration biopsy cytology underwent partial left mastectomy because the tumor was positive for adenocarcinoma cells in cytological diagnosis. Histologically, the specimen showed invasive adenocarcinoma growth, ductal and trabecular structure from the dermis to subcutaneous tissue. No neoplastic cells were present in the mammary gland and the definitive diagnosis was microcystic adenxal carcinoma (MAC) based on skin appendages. Conclusion : It is difficult to determine MAC in aspiration biopsy cytology of the breast in cytologic findings, and it is necessary to judge by clinical observation, image findings, and histological findings to reach a definitive diagnosis.