CK20

CK20 is a 46 kDa epithelial cytokeratin with more restricted expression than CK7 and shows characteristic staining patterns that aid in tumour classification. CK20 is most strongly associated with colorectal carcinoma, particularly early-stage disease and is positive in most lower gastrointestinal mucinous tumours and many urothelial carcinomas. Its CK7‑/CK20+ profile helps distinguish metastatic colorectal carcinoma from primary lung carcinoma, and it is also valuable in differentiating Merkel cell carcinoma (CK20 positive, dot‑like) from metastatic small cell lung carcinoma (CK20 negative). CK20 is less sensitive in poorly differentiated colonic carcinoma, and fixative type can affect interpretation (1).

Recommended Controls

Criteria for acceptable staining is a cytoplasmic staining pattern. The recommended controls to include normal colon, colon tumour, appendix or skin. Strong cytoplasmic staining of all surface epithelial cells in the appendix and colon as well as in the tumour cells. Tonsil will be negative.

Expected staining pattern

Urothelial tumour

Normal colon

Tonsil

Disclaimer

These methods are intended as a guide only. Laboratories that wish to implement these methods should perform internal validation/verification prior to use. The RCPAQAP does not make any claim or warranty for the accuracy or performance of these methods.