Multiple primary malignancies (MPMs) are a known phenomenon. We present a rare case of multicentric carcinoma of left breast synchronous with carcinoma of right lung. There was a diagnostic dilemma about the nature of the lung lesion, which otherwise would have been labeled as a metastasis from the breast primary; however, the immunohistochemistry markers distinguished between the two. The challenges in delivering radiotherapy in such not-so-conventional situations have been discussed. In spite of snag situation, patient can be treated safely with modern techniques and acceptable morbidities.