Cytokeratin 20 is a protein that is made mostly by cells in the colon, rectum, bladder, ureters, and urethra. It is also made by a specialized type of cell found in the skin called a Merkle cell.
Cytokeratin 20 is a type of protein called a keratin. These proteins are made mostly by cells on the surface of a tissue called epithelial cells. Another name for this protein is CK20.
Most tumours from the lower gastrointestinal tract and the genitourinary tract will produce cytokeratin 20. A type of tumour made up of Merkle cells called Merkle cell carcinoma will also produce this protein as will some tumours from the stomach and pancreas.
Pathologists perform a test called immunohistochemistry to look for cells producing cytokeratin 20. If the cells in your sample produce this protein, your report will describe the cells as positive or reactive. If they do not produce this protein, your report will describe the cells as negative or non-reactive.
This test is important if the tumour cells have traveled to a lymph node or distant body site or if the tumour cells look very abnormal. The movement of tumour cells to another part of the body is called metastasis. This test helps a pathologist decide where the tumour started.