Pulmonary nodules are a complicated issue and can be classified as benign nodules and malignant nodules based on CT presentation. The two most important diseases of malignant nodules are primary lung cancer and metastatic cancer, so for breast cancer patients, if a lung nodule is found, a CT scan is needed and the CT morphology is used to determine whether it is a benign nodule or a primary lung cancer or breast cancer metastasis. If the nodule cannot be determined based on CT, it needs to be combined with other imaging tools, such as PET-CT, and there is another important tool, which is to obtain a nodule specimen by puncture or surgery for pathological examination to finally determine whether it is metastasis or other diseases.