Definition

A condition in which abnormal cells are found in the lining of a breast duct (milk duct). Having ductal intraepithelial neoplasia may increase the risk of breast cancer in which these abnormal cells become cancer and spread outside the duct to other tissues in the breast. Types of ductal intraepithelial neoplasia include atypical ductal hyperplasia and ductal carcinoma in situ (DCIS). Also called DIN.