Histologic subtypes of ductal intraepithelial neoplasia (DIN) of the breast: Characteristic associations and biology

633 Background: Most invasive breast cancers are associated with more than one histologic subtype of DIN. The clinical and biologic significance of these DIN subtypes is under-appreciated. Methods: We reviewed 853 cases of DIN diagnosed at our University based Breast Center between 2003 and 2008, 568 (67%) of which were associated with an invasive cancer. Cases of pure invasive cancer without DIN were excluded. Results: A single histologic subtype was present in 41% of the cases, two subtypes in 43%, and three in 16%. The most common DIN subtypes present were solid (52%) and cribriform (50%), while the comedo (18%), micropapillary (11%), papillary (9%) and flat (6%) subtypes were less common. Comedo and solid DIN were frequently found together (Odds ratio [OR]) for coexpression 1.94, p< .001) as were micropapillary and papillary subtypes (OR 2.58, p< .005). Comedo DIN was much less likely to be found with papillary (OR .24, p< .005), flat (OR .34, p< .05), cribriform (OR .42, p< .001) or micropapillary (O...