Breast cancer is a malignant tumor that develops from the cells of
the breast. It is the most common type of cancer among women in
the United States. It is most often curable when found early. The
normal breast consists of three main components: the lobules
(milk-producing glands), the ducts (thin tubes that connect the
lobules to the nipple) and the stroma (fatty tissue and ligaments
surrounding the ducts and lobules, blood vessels, and lymphatic
vessels). About 80% of breast cancers start in the ducts.