Immunohistochemical profile of mucinous borderline tumors (MBT): INTESTINAL type: CK7 is strongly diffusely positive. MUC5AC, CEA and EMA are usually positive. CK20, CDX-2, and PAX8 are variably positive. ER and PR are negative. ENDOCERVICAL type: strongly positive for CK7, negative for CK20, CDX-2 and positive for ER, PR, WT-1, mesothelin, and CA-125. The image shows cytologic atypia in a MBT - intestinal type: The cyst wall of this MBT shows a complex glandular architecture. The lining epithelium is intestinal type mucinous tall columnar epithelium with basally located nuclei lacking atypia. The glands in the lower left show a greater degree of cytologic atypia; however, high-grade nuclear features are not present.