IMMUNOHISTOCHEMISTRY, CYTOKERATIN 20

What this test checks

Detects CK20 protein, which is characteristically expressed in colorectal cancer, gastric cancer, and Merkel cell carcinoma — used alongside CK7 to identify tumour origin.

Why do people get this test?

CK20 positivity strongly points toward colorectal or other specific cancer origins, helping oncologists identify where a cancer started when this isn't clinically obvious.

When you should consider this test

• When investigating cancer of unknown primary site
• When classifying gastrointestinal tumours
• As part of the CK7/CK20 tumour origin panel

How to prepare

No preparation needed — performed on biopsy or surgical tissue.