Introduction:?Although primary breast cancer is one of the most common malignancies in adult females, breast metastases from extramammary primary malignancies are rare accounting for approximately 0.4-1.3%. The primary sites are usually melanoma, hematologic malignancies, and lung cancer. Only a few cases of breast metastases from lung cancer in males have been reported. Gynecomastia is also an infrequent manifestation of lung cancer. To our knowledge, this is the first report of breast metastasis from small cell lung cancer in male patient with gynecomastia and treatment with palliative radiotherapy.?Case: A 56-year-old male, 37 pack-years smoker, presented with cough for 2 months. A chest computed tomography (CT) scan showed lung mass in the right upper lobe. Bronchoscopic biopsy specimens revealed small cell carcinoma. Immunohistochemical stains were positive for CD56, synaptophysin and transcription factor-1 (TTF-1), and negative for chromogranin. A positron emission tomography-CT scan and a brain magnetic resonance imaging study found no other metastatic lesion. He was diagnosed with limited-stage small cell lung cancer and received 2 cycles of chemotherapy (cisplatin and etoposide) plus concurrent radiotherapy, followed by 4 cycles of chemotherapy and prophylactic cranial irradiation. He was asymptomatic for next 2 years with no evidence of recurrence. In a routine follow-up visit, he complained of bilateral gynecomastia. On physical examination, a well movable round nodule was palpable at right subareolar area. A mammography and a chest CT scan showed 10 cm sized nodule in the right breast. An ultrasound-guided core needle biopsy was performed. The needle biopsy specimens revealed small cell carcinoma. Immunohistochemical stains were positive for CD56, synaptophysin and TTF-1, and negative for chromogranin. The histologic features were consistent with those of the previous biopsy specimens of his lung cancer. He refused to receive another chemotherapy and was treated with palliative radiotherapy to the right breast. A total dose of 3000 cGy was delivered in 10 fractions. His right breast nodule had improved until his death from progressive disease 10 months after breast irradiation.