Breast cancer is the abnormal growth of the cells that line the ducts and lobes of the breast. The classification of breast cancer is based on:

• Whether the cancer started in the ducts or the lobules of the breast.
• Whether the breast cancer cells have invaded other tissue in the breast.
• What the cancer cells look like under the microscope.

Classification also takes into consideration such information as how rapidly the cancer cells are multiplying (tumor grade) and whether breast cancer cells are present in the nearby lymph nodes.

The following classifications describe the most common types of breast cancer.

• In situ: A tumor that hasn't spread beyond the area where it began is called in situ.
  • Lobular carcinoma in situ (LCIS): Although not a true cancer, LCIS increases a woman's risk of developing cancer. For this reason, it's important for women with LCIS to have a physical exam 2 or 3 times a year, as well as a mammogram every year.
  • Ductal carcinoma in situ (DCIS): This is a precancerous condition also called Stage 0 breast cancer. It is noninvasive and is confined to the ducts. Nearly 100% of women with cancer at this stage can be cured.¹ The best way to detect DCIS is with a mammogram.
• Infiltrating (invasive) ductal carcinoma (IDC): This cancer starts in a milk duct, breaks through the wall of the duct, and invades the fatty tissue of the breast. From there, it can spread to other parts of the body. IDC is the most common type of breast cancer, accounting for nearly 80% of cases.
• Infiltrating (invasive) lobular carcinoma (ILC): This cancer starts in the mammary, or milk, glands (lobules) and can spread to other parts of the body. About 10% of breast cancers are this type.