CK20 is a protein that is made mostly by cells in the colon, rectum, bladder, ureters, and urethra. CK20 is also made by a specialized type of cell found in the skin called a Merkle cell.
CK20 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 CK20 is cytokeratin 20.
Most tumours from the lower gastrointestinal tract and the genitourinary tract will produce CK20. A type of tumour made up of Merkle cells called Merkle cell carcinoma will also produce CK20 as will some tumours from the stomach and pancreas.
Pathologists perform a test called immunohistochemistry to look for cells producing CK20. If the cells in your sample produce CK20, your report will describe the cells as positive or reactive. If they do not produce CK20, your report will describe the cells as negative or non-reactive.
Why is this important? 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.