Abstract / Summary
BackgroundMale breast cancer (MBC) is rare, accounting for approximately 1% of all breast cancers. When MBC is diagnosed simultaneously with a second primary lung cancer, treatment planning becomes particularly complex because diagnostic certainty, technical resectability, competing treatment windows, and radiotherapy safety must all be considered.Case presentationWe report a 72-year-old man who was synchronously diagnosed with left invasive ductal breast carcinoma and right lower lobe poorly differentiated non-small cell lung cancer (NSCLC). The breast cancer was staged as pT3N2aM0, AJCC 8th edition stage IIIA, with strong ER/PR expression and HER2 nonamplification. The lung lesion was pathologically diagnosed as poorly differentiated NSCLC without definitive glandular, squamous, or neuroendocrine differentiation and was staged as cT3N0M0, AJCC 8th edition stage IIB. Although stage IIB NSCLC is usually evaluated for surgery, this tumor closely involved the right lower lobe pulmonary vessels and bronchial structures, and thoracic surgeons considered upfront radical resection technically unsafe because of the risks of hemorrhage, extended resection, impaired blood supply to the remaining lobes, and loss of pulmonary function. After multidisciplinary team (MDT) discussion, the patient underwent left modified radical mastectomy, adjuvant AC-T chemotherapy, and simultaneous postmastectomy radiotherapy to the left chest wall/regional nodes with definitive radiotherapy to the right lung lesion plus concurrent cisplatin. Imaging shortly after radiotherapy showed marked shrinkage of the right lung lesion, but subsequent CT and liver MRI suggested systemic progression with multiple hepatic lesions. The patient declined liver biopsy, received one cycle of vinorelbine plus cisplatin with Endostar, discontinued further treatment, and died of liver failure in March 2026.ConclusionThis case illustrates that therapeutic prioritization in synchronous double primary cancers should not be determined solely by TNM stage or chronological order of diagnosis. Instead, treatment decisions should integrate pathological distinction, tumor biology, anatomical treatability, technical resectability, curative potential, competing treatment windows, and short-term clinical threat. In selected patients, simultaneous postmastectomy radiotherapy and definitive lung radiotherapy may be feasible when supported by MDT consensus, dosimetric review, and close toxicity monitoring.