The distinction between primary ovarian mucinous carcinoma and mucinous mCRC is more difficult, and IHC is less helpful, because primary ovarian mucinous adenocarcinomas often exhibit intestinal differentiation and may be positive for CK20, but also for CEA, CDX2, and CA19-9 [38, 64]; conversely, some mucinous mCRC may be positive for CK7, in which case it is the most useful marker. The gene discussed is CDX2; the disease is ovarian mucinous adenocarcinoma.