Le Zhang,1 Chenghua Zhang,2 Zhaoying Yang,1 Miao He,3 Lijuan Zhang,1 Shereen Ezzat,4 Xi Liang5 1Department of Breast Surgery, China-Japan Union Hospital, Jilin University, Changchun, Jilin, China; 2Endoscopy Department, Jilin Cancer Hospital, Changchun, Jilin,China; 3Department of Anesthesia, The Second Hospital of Jilin University, Changchun, Jilin, China; 4Ontario Cancer Institute and The Endocrine Oncology Site Group, Princess Margaret Hospital, University Health Network, Toronto, Ontario, Canada; 5Department of Breast Surgery, The Second Affiliated Hospital of Dalian Medical University, Dalian, Liaoning, China Abstract: Occult breast cancer is defined by the presence of axillary metastases without an identifiable primary breast tumor. Here, we report a rare case of a male occult breast cancer with dermatomyositis. We performed a modified radical mastectomy consisting of whole breast mastectomy and axillary lymph node dissection. Immunohistochemistry and fluorescent in situ hybridization analyses demonstrated an adenocarcinoma likely of breast origin, which was an occult triple-negative breast cancer. Interestingly, the patient’s previously noted periorbital dermatomyositis resolved promptly following surgical excision. Keywords: male breast cancer, occult breast cancer, triple-negative breast cancer, dermato­myositis