A male with primary accessory breast carcinoma in an axilla is strongly suspected of having hereditary breast cancer.

We herein report on a male with primary accessory breast cancer in an axilla. A 75-year-old man first noticed a subcutaneous nodule about 2 cm in diameter in the area of his right axilla. The patient underwent extirpation of the mass in a public hospital. Histological examination revealed invasive breast carcinoma of no special type associated with mucinous carcinoma, invasive micropapillary carcinoma and intraductal components. Immunohistochemical analysis showed that the tumor cells were positive for Gross cystic disease fluid protein (GCDFP)-15, mammaglobin and GATA3. Staining for estrogen receptor (ER) and progesterone receptor (PR) was positive, and human epidermal growth factor receptor 2 (HER2) was negative. The Ki67 labeling index (LI) was 33.6%. Imaging revealed no evidence of a primary tumor in any other organ or in the bilateral mammary gland. We performed radical resection of the right axilla, including the scar, and axillary lymph node dissection. The final pathological examination of the surgical specimen showed normal mammary gland tissue that was not connected to the proper mammary gland, and no residual cancer or metastatic lymph nodes. Based on our clinical and pathological findings, this tumor was diagnosed as breast cancer originating from the accessory mammary gland in the right axilla. After surgery, tamoxifen was administered as adjuvant therapy. Since the surgery, 2 years ago, there has been no evidence of recurrence. Hereditary Breast and Ovarian Cancer syndrome was suspected in this case because the patient was a male with breast cancer, and he had two first-degree relatives with breast cancer. This patient had no BRCA mutations on genetic testing. Nonetheless, in cases of male breast cancer, it is necessary to obtain genetic information due to the possibility of hereditary breast cancer, including cancers associated with BRCA gene mutation.