Carcinoma In Situ is used to describe breast cancer that has not yet spread beyond the ducts or lobes where it began. While it is not considered invasive, this diagnosis does mean that changes have taken place in your body that show that you are at risk for developing invasive cancer. There are two types of carcinoma in situ. One arises in the ducts (the pipelines to the nipple), and is named Ductal carcinoma in situ. The other arises in the lobes (the milk-producing tissue), and is called Lobular carcinoma in situ. In situ cancers, when detected and treated early, are rarely life-threatening.

Ductal Carcinoma in situ: is much more common than lobular carcinoma in situ, and can grow into invasive cancer if not detected at an early stage.

Lobular Carcinoma in situ: is actually called a "pre-cancer," and is considered a high-risk factor for breast cancer.