Breast cancer is approximately 100 times less common among men. Estrogen-related receptor α was detected in human prostate cancer tissue, and androgen receptors are expressed in both normal and malignant breast tissue. Thus, prostate cancer hormonal therapy may increase breast cancer risk. A 67-year-old man with prostate cancer history presented with rising prostate-specific antigen level. F-Fluorocholine PET/CT showed intense uptake in his right breast and moderate uptake in right axillary lymph node. Complementary F-FDG PET/CT demonstrated more intense tracer uptakes in both the right breast and axillary lymph node. Breast histological findings were invasive ductal cancer, with axillary lymph node invasion.