If a lung nodule is found in breast cancer, first of all, it depends on whether the nodule has been found before, whether it is new or original. Generally, for small lung nodules, the diameter of which is less than 5mm, you can first observe the nodules regularly, mainly by doing lung CT in 3 months to 6 months to observe whether there is any change in the nodules. If there has been no change, no special treatment is needed. If the nodule is between 0.5-1 cm, it needs to be identified as benign or malignant. An enhancement test can be done to see if there is any change in the nodule, and if it suggests malignancy, surgery may be needed. If a benign lesion is considered, it is also followed by regular review. For lung nodules larger than 1 cm in diameter, it is recommended to take pathological examination to confirm the diagnosis, such as a percutaneous lung aspiration biopsy or bronchoscopy for pathology. If this is not possible, thoracoscopic resection of the nodule may be required to obtain pathology to confirm the diagnosis. This nodule may recur or it may be metastatic from breast cancer, so systemic chemotherapy is needed to control the disease.