First report of bilateral synchronous male accessory breast cancer

Accessory breast occurs due to the persistence of milk line in the non-thoracic region. Malignant transformation in male accessory breast is very rare, with 16 reports documented across the world. No bilateral synchronous accessory male breast cancer has been reported. We present the first case reported globally of a man in his 70s with a complaint of left axillary lump and chronic rash for 3 years. About 1 year ago, additional reddish rash was detected in the right axilla. Initial skin biopsy from a private hospital confirmed mammary carcinoma with skin invasion. Subsequent left breast mastectomy with left axillary lymph node dissection and right wide excision was performed. Final pathological result was grade 2 invasive ductal carcinoma in the left accessory breast and Paget's disease in the contralateral axilla. Postoperative treatment of adjuvant paclitaxel and trastuzumab was prescribed, which was followed by adjuvant radiation therapy.