Ductal carcinoma in situ (DCIS or intraductal carcinoma) is a very early form of noninvasive breast cancer that begins in the lining of the small milk ducts that drain milk out of the breast through the nipple. It usually does not cause a lump in the breast and is seen as small calcium deposits (microcalcifications) on a mammogram.

Most experts consider DCIS a precancerous condition that may progress to invasive breast cancer. Unfortunately, doctors do not know how to tell which cases of ductal carcinoma in situ will progress and which will not.

Treatment options for DCIS include mastectomy or lumpectomy with radiation. The medication tamoxifen may be used to reduce the risk of future breast cancer.