Some clues in the immunostaining patterns with cytokeratins in a cutaneous mestastasis of carcinoma of unknown origin

(If you need basic information on what keratins are: see here)

CK7+/CK20+: if CK7 is more intense than CK20, consider lung. Perform TTF1. Other: urothelial, pancreatic, cholangiocarcinoma, some gastric, ovary, small intestine. PAX-8 is positive in a big number of urothelial and ovarian carcinomas.

CK7-/CK20+: Colorectal carcinoma(75-81 % are CK7-, CK20+, but 10-16 % are CK7+/CK20+ and 4-15 % are CK7-/CK20-). Also perform CDX2.

CK7-/CK20-: not very orientative pattern.

CK7+/CK20-: Lung (72-86%; but 6-17% are CK7-/CK20- and 6-11% are CK7+/CK20+). Breast, ovary, prostate. Billiary carcinoma. Gastric (rare).