Intraepithelial carcinoma in a mucinous borderline tumor (MBT)of the ovary: MBT generally shows mild to moderate cytologic atypia in the lining epithelium. When the glands or papillary structures are lined by cytologically malignant cells and the atypia is confined to the epithelium (i.e. no invasion of the underlying stroma), the term "intraepithelial carcinoma" is applied. This image shows a mucinous borderline tumor of intestinal type in which the glands are lined entirely by signet ring cells (an unusual feature; same case as images 40-42)). The glands on the right completely lack cytologic atypia, where as the glands on the left are malignant and show severe cytologic atypia consisting of irregularly enlarged hyperchromatic nuclei with prominent nucleoli. There is no evidence of stromal invasion. The prognosis is excellent if the cytologic atypia is confined to the surface epithelium and stromal invasion has been definitively excluded by a thorough sampling of the tumor.