The main reasons for breast cancer treatment to be chemotherapy first and then surgery are as follows: 1. to detect the sensitivity of breast cancer to chemotherapy drugs, if the patient undergoes resection and then chemotherapy, the doctor cannot determine the sensitivity of breast cancer to chemotherapy drugs, preoperative chemotherapy for breast cancer, if the lump shrinks, the breast cancer can be considered sensitive to chemotherapy drugs; if the breast cancer does not shrink after using the chemotherapy drug, it is considered that the breast cancer is not sensitive to the drug If the breast cancer does not shrink after chemotherapy, the breast cancer is considered insensitive to the drug and needs to be replaced by another chemotherapy regimen; 2. The shrinkage of the mass after chemotherapy can downgrade the clinical stage and reduce the scope of surgery, and some patients who cannot undergo breast-conserving surgery can undergo breast-conserving surgery after chemotherapy due to the shrinkage of the mass to maintain a better breast appearance.