Ductal carcinoma in situ is breast cancer, which is the most common type of non-invasive breast cancer and belongs to early stage cancer. Ductal carcinoma in situ is not life-threatening. Ductal carcinoma in situ means that the cancerous tissues have not spread to the surrounding normal breast tissues, and the cancerous tissues are confined to the ducts of the breast, but the chance of developing invasive carcinoma of the breast is significantly higher than that of the patients who did not have carcinoma in situ before. Since ductal carcinoma in situ is confined to the ducts without infiltration, it is usually treated with lumpectomy plus radiotherapy, mastectomy, simple lumpectomy, lumpectomy plus hormone according to the medical conditions and the patient’s wishes. In the presence of ductal carcinoma in situ, patients should go to the hospital regularly for follow-up ultrasound, molybdenum target, nuclear magnetic resonance imaging, etc., to rule out whether other glandular tissues have produced new ductal carcinoma in situ.