Breast cancer that starts in a milk duct of the breast.

Mammary ductal carcinoma is breast cancer that starts in the milk ducts of the breast. It includes ductal carcinoma in situ, which means the cancer cells are confined inside the milk duct. In invasive ductal carcinoma, the cancer cells break out of the duct and spread into the breast tissue.

Symptoms include a lump or thickened area in the breast that feels different from the breast tissue around it. Other symptoms include nipple discharge, a nipple that turns inward and changes in the size, shape and appearance of the breast.

Treatments might include surgery, radiation and medicines. Medicines used for breast cancer include chemotherapy, hormone therapy, targeted therapy and immunotherapy.