MONDO_0004007 (breast intraductal proliferative lesion) is a group of non-invasive epithelial proliferations that occur in the ductal system of the breast. The vast majority of cases arise in the terminal ductal lobular units. This category includes atypical ductal hyperplasia, usual ductal hyperplasia, flat epithelial atypia, and ductal carcinoma in situ. There is an increased risk for subsequent development of invasive breast carcinoma. Also known as: DIN, ductal intraepithelial neoplasia, intraductal proliferative lesion, intraductal proliferative lesion of the breast, mammary intraepithelial neoplasia, ductal type.