Axillary lymph node metastasis as the first manifestation of male occult breast cancer: A Case Report

RATIONAL: Occult breast cancer (OBC) is an extremely rare breast cancer and is defined by the presence of axillary metastasis without a primary tumor in the breasts or any abnormality on radiologic examination. PATIENT CONCERNS: This case report presents a 49-year-old man who was diagnosed with male OBC, which first manifested as an axillary lymph node metastasis followed by the emergence of infraclavicular lymph node metastasis. Neither the breast nor other organs had any abnormality. DIAGNOSIS: The pathological examination revealed metastatic adenocarcinoma. Immunohistochemical (IHC) staining results were positive for estrogen receptor (ER), progesterone receptor (PR), and gross cystic disease fluid protein-15 (GCDFP-15); and negative for human epidermal receptor-2 (Her-2) 1+, cytokeratin (CK) 7, CK20, and thyroid transcription factor-1 (TTF-1). INTERVENTIONS: The patient underwent left axillary lymph node dissection but not a mastectomy. After the operation, the patient subsequently underwent chemotherapy, radiotherapy, and endocrinotherapy. OUTCOMES: Currently, he has been followed-up for >4 years without any signs of recurrence. LESSONS: Careful physical and imaging examinations combined with pathological analysis are essential in the diagnosis of male OBC. Early surgery remains the primary treatment.