Case Report: Synchronous double primary male breast cancer and non-small cell lung cancer: diagnostic confirmation and multidisciplinary management.

Background: Male 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 presentation: We 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 pT Conclusion: This 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.