Mammary ductal carcinoma is the most common type of breast cancer in women. It comes in two forms: invasive ductal carcinoma (IDC), an infiltrating, malignant and abnormal proliferation of neoplastic cells in the breast tissue, or ductal carcinoma in situ (DCIS), a noninvasive, possibly malignant, neoplasm that is still confined to the milk ducts, where breast cancer most often originates. Some doctors feel that DCIS is overdiagnosed and that many women who are treated for DCIS do not actually have cancer.