Primary mucinous carcinomas of ovary show strong diffuse positivity for CK7; however, several tumors such as adenocarcinomas of pancreas, stomach, gall bladder, small bowel, appendix, and lung that can present clinically as primary ovarian tumor are also variably positive for CK7. Mucinous borderline tumors and ovarian carcinomas can show weak and focal positivity for CK20 in 65-75% of cases. Colorectal adenocarcinomas, on the other hand, are strongly diffusely positive for CK20. A CK7-negative/CK20-positive profile is highly suggestive of metastatic colorectal adenocarcinoma (caveat: right-sided colonic adenocarcinomas and poorly-differentiated tumors may be CK20-negative). Other markers that are positive in mucinous ovarian carcinomas include CA-125, MUC5AC, and DPC4. The image shows mucinous carcinoma with destructive stromal invasion. The invasive foci are composed of distorted glands, isolated tumor cells, and small nests or clusters of cells with high-grade nuclear features that are haphazardly infiltrating desmoplastic stroma.