Ductal carcinoma in situ. A noninvasive condition in
which abnormal cells are found in the lining of a breast duct. The abnormal
cells have not spread outside the duct to other tissues in the breast. In
some cases, DCIS may become invasive cancer and spread to other tissues,
although it is not known at this time how to predict which lesions will
become invasive. Also called ductal carcinoma in situ and intraductal carcinoma.