DCIS (ductal carcinoma in situ; also called intraductal carcinoma) is a condition in which cancer cells are contained within the ducts of the breast. In DCIS, the cancer cells have not invaded the surrounding fatty and connective tissue of the breast, nor have the cancer cells spread to other parts of the body.
Fortunately, DCIS is very curable. For example, almost all women who are diagnosed with DCIS and treated early survive at least 5 years post diagnosis.
In contrast, invasive breast cancers occur when cancer cells move beyond a duct or lobule into the surrounding fatty or connective tissue of the breast. As invasive cancers become more advanced, the cancer cells can spread through the blood or lymphatic system to other organs in the body.
If not treated, nearly one-fourth of all DCIS cases can develop into invasive breast cancer within 5 to 10 years. Such invasive forms of breast cancer are much more difficult to cure.