Carcinoma in situ of the breast cannot be left untreated; untreated carcinoma in situ of the breast can develop into invasive carcinoma, which can jeopardize the patient’s life. Carcinoma in situ of the breast will not heal by itself and cannot be left untreated. This is because if patients do not take timely measures to treat it, it may develop into invasive carcinoma, with symptoms such as painless breast lumps, breast skin abnormalities, bloody or plasmatic nipple overflow, and enlarged axillary lymph nodes. In addition, if patients present with carcinoma in situ of the breast without timely treatment, it will also metastasize to lungs, bones and other organs. If carcinoma in situ of breast metastasizes to lungs, patients will have cough, dyspnea, hemoptysis, chest pain and other symptoms. If breast carcinoma in situ metastasizes to bones, it will manifest as bone pain. Patients who have breast carcinoma in situ usually cannot not take measures to treat it, and they need to seek medical treatment in time and can choose appropriate measures under the guidance of doctors.