Ductal carcinoma in situ is a malignant tumor at the beginning. 1. Ductal carcinoma in situ, i.e. intraductal carcinoma of the breast, is a kind of non-invasive breast cancer, which means that the cancer cells are located in the ducts of the breast and have not yet broken through the basement membrane of the duct wall. Non-invasive breast cancer is an early stage breast cancer with better prognosis. 2. The etiology of breast cancer has not been clearly defined, and it is currently believed that there is a direct relationship between the onset of breast cancer and estrone and estradiol. In addition, early age of menarche, late age of menopause, infertility, late age of the first full-term delivery, environment and lifestyle also have a certain relationship with the onset of breast cancer. Whether benign breast lesions are related to the development of breast cancer has not yet been confirmed. 3. Experiments show that if no treatment is given to ductal carcinoma in situ diagnosed by biopsy, 30% of it can develop into invasive breast cancer with poor prognosis after 20 years. Therefore, it should be treated at an early stage once diagnosed. Breast cancer is mainly treated with a comprehensive strategy based on surgery.