Cytokeratin 20 (CK20)

November 5, 2023

Cytokeratin 20 (CK20) is a protein made by epithelial cells in the colon and urinary tract. It is also made by Merkle cells in the skin. This type of protein is also made by most benign (noncancerous) and malignant (cancerous) tumours that start in the colon and urinary tract and in a type of skin cancer called Merkle cell carcinoma. After CK20 is made, it is held in the cytoplasm (body) of the cell. CK20 is a structural protein that helps epithelial cells maintain their shape.

Immunohistochemistry (IHC) is a test pathologists perform to see CK20-producing cells in a tissue sample. When combined with other immunohistochemical markers, this test allows pathologists to determine if the cells they are seeing under the microscope come from one of the organ systems that normally produces this protein. Cells that produce CK20 are typically described as ‘positive’ while those that do not produce the protein are described as ‘negative’.

This test is particularly helpful when examining a tumour under the microscope because tumours that come from the colon and urinary tract are more likely to produce CK20 while tumours from other locations are not. Pathologists use the results of this test combined with other features to make a diagnosis.

Examples of tumours that are positive for cytokeratin 20:

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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