Breast cancer originates from all levels of ducts and glandular epithelium, and the process of development is from glandular epithelial hyperplasia → atypical hyperplasia → carcinoma in situ → early invasive carcinoma → invasive carcinoma, and the abnormal proliferation of glandular epithelial cells is the basis for the occurrence and development of breast cancer. The ducts and alveoli of the breast are composed of two layers of cells, namely the inner layer of glandular epithelial cells and the outer layer of myoepithelial cells (MEC), which form the basal cell layer of the normal breast epithelial structure. MEC deficiency in the breast is an important reference for diagnosing ductal, lobular hyperplasia or carcinoma in situ, papilloma or papillary carcinoma, carcinoma in situ or invasive carcinoma, benign pseudo-infiltrative lesion or cancerous infiltrate, etc. Immunohistochemistry (e.g., myoepithelial staining) often provides a valuable reference for differential diagnosis. Ki67 is a murine monoclonal antibody to the crude nucleus of the L428 cell line produced by Hodgkin’s lymphoma. Ki67 protein is present in the nucleus of proliferating cells and is a non-histone nuclear protein consisting of two multi-skin chains of 345kd and 395kd, encoded by two articulated mRNAs of 9768bP and 395bp, respectively. Ki67 antigen appears in mid to late Gl phase, gradually increases in S and G:phases, and reaches its highest value in M phase, and is rapidly degraded or loses its antigenic determinant cluster after M phase. its half-life is short and it is rapidly degraded after the cell leaves the proliferative cycle. pki67 undergoes phosphorylation and dephosphorylation during mitosis before it is susceptible to protease hydrolysis, and its structure implies that its expression is regulated by protease bypass. ki67 has a complex localization form in the Ki67, a proliferating cell nuclear protein associated with the cell cycle, reacts only with proliferating cell nuclei without tissue specificity and is a valuable marker for defining apoptosis and proliferation. Ki67 accurately reflects the proliferative activity of tumor cells and is associated with the development, metastasis and prognosis of many tumors, except Ki67 can reflect the proliferative activity of tumor cells directly and sensitively, and can reflect the number of proliferating cells more comprehensively. The combination of Ki67 and other tumor molecular markers can better reflect the proliferative activity of tumor, and is of great importance in determining the malignancy, prognosis and postoperative adjuvant therapy. In breast cancer with large primary lesions, axillary lymph node metastasis and late UICC stage, the positive expression rate of Ki67 is statistically significant, and its high positive expression can reflect the strong proliferation and invasive ability of tumor cells and high malignancy. In invasive breast cancer, Ki67 was found to be closely related to tumor cell proliferation and invasive metastasis. Ki67 expression is associated with the clinical stage of breast cancer, i.e. the more advanced the stage, the higher the Ki67 positivity rate. Ki67 is proportional to the malignancy of the tumor and is closely related to the growth, invasion and metastasis of the tumor, which is an important index for the diagnosis and prognosis of breast cancer. High Ki67 expression is an indicator of poor prognosis of breast cancer. High Ki67 expression is an indicator of poor prognosis of breast cancer. Ki67 can also be used as an indicator of breast cancer chemotherapy sensitivity. The decrease of tumor cell proliferation rate. It is a better indicator of tumor sensitivity to chemotherapy than tumor mass shrinkage. It has been demonstrated that the comparison of ki67 expression in breast cancer tissues of different therapeutic groups before and after NACT:The percentage of Ki67 positive cells positive area in breast cancer tissues of the group in complete clinical remission after NACT was significantly decreased compared with that before NACT, and the difference was statistically significant (P<0.01)< span="">. Normal tissue and organ cells are in dynamic balance between proliferation and apoptosis under the regulation of many factors, while the occurrence of malignant tumors depends to a great extent on the balance and transformation of cell proliferation and apoptosis. When tumor cells proliferate and apoptosis regulation is abnormal, i.e. proliferation is greater than apoptosis, tumor may develop. On the contrary, the tumor will shrink or even die out. Studies have confirmed that most chemotherapeutic drugs remove tumor cells by inhibiting cell proliferation and inducing apoptosis. After tumor cells are hit by chemotherapeutic drugs, their growth and proliferation are inhibited and apoptosis increases, and the more sensitive tumor cells are to chemotherapy, the more obvious the inhibition of proliferative state is. Because Ki67 is the most used marker to understand the proliferation status of tumor cells, it fully reflects the proliferation status of tumor cells, and the more obvious the decrease of Ki67, the more certain the efficacy of chemotherapy. Therefore, it can be concluded that Ki67 can not only reflect the proliferation status of tumor cells, but also may be an important reference marker for the evaluation of NACT efficacy. Meanwhile, few studies have reported that Ki67 is expressed in normal breast tissue, and samples from normal breast or fibroadenoma and hyperplastic epithelium show extremely low levels of ki67 expression. Although there are many tools available to determine the prognosis of breast cancer: breast cancer stage, grade, histological type, estrogen and progesterone receptor status, DNA ploidy, CerbB-2 expression, and breast cancer risk factor prediction models, there are still many patients who cannot receive adequate treatment because the current predictive tools are not ideal for determining the prognosis, resulting in early recurrence and metastasis, and quality of survival and However, many patients are still unable to receive adequate treatment because the current prediction tools are not ideal to determine the prognosis, resulting in early recurrence and metastasis, and the quality and duration of survival are not guaranteed. Many studies have shown that Ki67 marker index can reliably reflect the proliferative activity of normal and diseased lesions, and it can be used as an auxiliary indicator for the differentiation of benign and malignant diseases, as well as for the prediction of the possibility of cancer in benign lesions, early diagnosis of malignant tumors, selection of treatment methods and evaluation of efficacy.