Breast metastases from an extramammary primary tumor are very rare, particularly in men. In this study, we present a case of a 74-year-old man with isolated breast metastasis from lung adenocarcinoma as an incidental finding on PET/CT and diagnosed concomitantly with the primary tumor. Detection of isolated incidental metastatic lesions in the breast on PET/CT imaging has a significant clinical impact on patients with known malignant disease due to change of disease stage, management, and also treatment method.