There is a big difference between primary and secondary breast cancer. Primary breast cancer is a malignant tumor that originates in the breast, such as ductal or lobular carcinoma, both of which are malignant tumors that originate in the breast. Secondary breast cancer refers to the metastasis of tumors elsewhere to the breast, such as metastasis to the breast from lung cancer, metastasis to the breast from colorectal cancer, metastasis to the breast from liver cancer, etc. The treatment strategy for metastatic breast cancer is completely different from that of primary breast cancer. The treatment of primary breast cancer is based on surgical resection, and after surgery, radiotherapy, chemotherapy, endocrine therapy or targeted therapy will be done according to the postoperative pathology. The treatment of secondary breast cancer depends on the treatment of the primary tumor, the location and number of metastatic tumors in the breast, and whether radical surgery can be performed.