In addition, there are two types of breast tumors that are not cancer but increase the risk of breast cancer: Ductal carcinoma in situ (DCIS) â DCIS is a condition in which abnormal cells are found in the lining of breast ducts. These cells have not spread outside the duct to the surrounding breast tissue. But some cases of DCIS become breast cancer over time. So DCIS is sometimes called Stage 0 breast cancer.