Carcinoma in situ of the breast can be cured because carcinoma in situ of the breast rarely metastasizes. It is conceivable that breast cancer occurs in the epithelial cells of the breast duct, just like it occurs in a duct. If the tumor does not break through the wall of the duct, that is, the basement membrane of the breast duct, it is called carcinoma in situ. If the tumor does not break through the duct wall, that is, the basement membrane of the duct, it is called carcinoma in situ. Once it breaks through the duct wall, it may develop lymphatic or hematologic metastasis. Theoretically, it is impossible for metastasis to occur in situ, so as long as all areas of breast cancer in situ can be removed by surgery, it can be cured. However, whether breast cancer in situ can be preserved or not may not be related to whether it is in situ or invasive cancer, but depends on the extent of the in situ or invasive cancer. There are many breast carcinomas in situ that are particularly extensive, and even in situ carcinoma requires total excision of the breast in order to be cured. It is not like some people mistakenly believe that in situ carcinoma can preserve breast while invasive carcinoma cannot.