According to the need of treatment, breast cancer can be divided into 5 categories: 1. simple non-invasive carcinoma (lobular carcinoma in situ and ductal carcinoma in situ) 2. operable locally invasive carcinoma (clinical stage I, II and some stage IIIA) 3. inoperable locally invasive carcinoma (some stage IIIA, IIIB and IIIC) 4. metastatic or recurrent breast cancer (stage IV) 5. special types of breast cancer The following is a description of the above 5 types The treatment of breast cancer is described separately. Simple non-invasive carcinoma Simple non-invasive carcinoma includes lobular carcinoma in situ and ductal carcinoma in situ, both of which are sometimes difficult to distinguish from atypical hyperplasia or early invasive carcinoma. Therefore, pathological examination should be performed in all cases. Patients with simple non-invasive carcinoma should undergo bilateral mammography to check for the presence of multiple primary tumors and to assess the extent of non-invasive lesions. The goal of treatment for simple non-invasive carcinoma is to prevent the appearance of infiltrative lesions or to detect their infiltrative component while they remain confined to the breast. Patients with invasive carcinoma (even if it is microinfiltrative) found during the examination should be treated as invasive breast cancer. 2. Lobular carcinoma in situ Patients with lobular carcinoma in situ have a low risk of developing invasive carcinoma, and death from secondary invasive carcinoma is rarely seen. Therefore, for patients with lobular carcinoma in situ, only follow-up observation and review once every six months is sufficient. Only for special high-risk patients, such as those with a family history of breast cancer and BRCA1/2 mutation, bilateral total mastectomy combined with or without breast reconstruction should be considered. Patients with lobular carcinoma in situ have an equal risk of invasive breast cancer in both breasts, therefore, if total mastectomy is considered bilateral total mastectomy is required. Recent data show that oral tamoxifen for 5 years significantly reduces the incidence of invasive breast cancer in patients with lobular carcinoma in situ who choose to be followed up and observed. Ductal carcinoma in situ For most patients with ductal carcinoma in situ with limited lesions, either “lesion excision + whole breast radiotherapy” or “total mastectomy with or without breast reconstruction” is the appropriate treatment option. Axillary lymph node dissection is not recommended for patients with ductal carcinoma in situ. The addition of radiotherapy to breast-conserving surgery for pure lesion excision can significantly reduce the local recurrence rate; total mastectomy itself is an effective measure to reduce the risk of local recurrence. There is no difference in survival between the two treatments. Patients who opt for breast-conserving surgery should have postoperative x-rays of the affected breast and surgically excised specimens to ensure that all lesions have been removed. Similar to lobular carcinoma in situ, oral tamoxifen is recommended for 5 years after surgery for patients with ductal carcinoma in situ to reduce the risk of recurrence and the development of invasive breast cancer.