The expression of CK7, when combined with CK20 expression, can be used to determine primary origin.[14] A previous study showed that for CK7+ tumors, the staining distribution of CK7 was frequently diffuse (in > 50% of positive tumor cells) in primary ovarian, upper gastrointestinal tract (including pancreatobiliary tract), and endocervical tumors, whereas the CK7 staining distribution was often focal (in < 50% of positive tumor cells) when present in colorectal and appendix carcinomas.[15]. Here, KRT7 is linked to appendix carcinoma.