Background: Differentiating pulmonary metastasis from primary lung cancer can be challenging in patients with breast malignancy. This study aimed to characterize the imaging features of 18fluorodeoxyglucose‐positron emission tomography/computed tomography (18F‐FDG‐PET/CT) for distinguishing between these diseases. Methods: We enrolled 52 patients who received curative treatment for breast cancer but later presented with suspected solitary pulmonary lesions (SPLs) and subsequently underwent 18F‐FDG‐PET/CT to investigate. Results: Subsolid lesions, ill‐defined borders, lung lesions with negative maximum standardized uptake value, and lesions without 18F‐FDG‐PET/CT‐diagnosed hilar and/or mediastinal lymph nodes and pleural metastases were more likely to be associated with primary lung cancer. Conclusions: CT border, FDG uptake, hilar and/or mediastinal lymph node metastasis, and pleural metastasis are potential markers for diagnosis. [ABSTRACT FROM AUTHOR]