Ductal carcinoma in situ (DCIS) means the cells that line the milk ducts of the breast have become cancer, but they have not spread into surrounding breast tissue. DCIS is considered non-invasive or pre-invasive breast cancer. DCIS can’t spread outside the breast, but it still needs to be treated because it can sometimes go on to become invasive breast cancer (which can spread). See Breast Cancer for signs, symptoms and treatments.
