Male accessory breast mucinous carcinoma: a case report and literature review

Accessory breast carcinoma represents a distinct ectopic malignancy comprising approximately 0.3-0.6% of all mammary neoplasms, of which male accessory breast cancer is even rarer. This condition typically manifests as a progressively enlarging mass, predominantly situated in the axillary or inguinal regions, and may present with early lymph node metastasis. Pathological examination remains the diagnostic gold standard, whereas ultrasound, mammography, and MRI serve as critical adjunctive modalities. Current therapeutic strategies for accessory breast carcinoma largely mirror established breast cancer protocols, establishing surgical resection as the cornerstone, followed by adjuvant endocrine therapy, chemotherapy, and radiotherapy. Here, we report a case of a 72-year-old male with accessory breast cancer. The patient was diagnosed with right axillary accessory breast cancer with right axillary lymph node metastatic cancer in 2021 and underwent right accessory mastectomy plus right axillary lymph node dissection at our hospital. Postoperatively, the patient completed adjuvant chemotherapy and remains on maintenance endocrine therapy. In 2025, a follow-up examination revealed a new mass in the medial aspect of the right upper arm near the axilla. Histopathological evaluation of the excised specimen confirmed features consistent with mucinous breast carcinoma. This report seeks to heighten clinical vigilance regarding male accessory breast carcinoma by providing a comprehensive delineation of its diagnostic trajectory, clinical progression, and therapeutic management in an exceptionally rare presentation.