Tumor antigen

Tumor antigen is an antigenic substance produced in tumor cells, i.e., it triggers an immune response in the host. Tumor antigens are useful tumor markers in identifying tumor cells with diagnostic tests and are potential candidates for use in cancer therapy. The field of cancer immunology studies such topics.

Mechanism of tumor antigenesis

Normal proteins in the body are not antigenic because of self-tolerance, a process in which self-reacting cytotoxic T lymphocytes (CTLs) and autoantibody-producing B lymphocytes are culled "centrally" in primary lymphatic tissue (BM) and "peripherally" in secondary lymphatic tissue (mostly thymus for T-cells and spleen/lymph nodes for B cells). Thus any protein that is not exposed to the immune system triggers an immune response. This may include normal proteins that are well sequestered from the immune system, proteins that are normally produced in extremely small quantities, proteins that are normally produced only in certain stages of development, or proteins whose structure is modified due to mutation.

CA19-9

CA 19-9 (carbohydrate antigen 19-9, also called cancer antigen 19-9 or sialylated Lewis (a) antigen) is a tumor marker that is used primarily in the management of pancreatic cancer. CA 19-9 is an antigen defined by monoclonal antibody binding to CA 19-9, the tumor surface marker Sialyl-Lewis A.

History

CA 19-9 was discovered in the serum of patients with colon cancer and pancreatic cancer in 1981.

Uses

Guidelines from the American Society of Clinical Oncology discourage the use of CA 19-9 as a screening test for cancer, particularly pancreatic cancer. The reason is that the test may be falsely normal (false negative) in many cases, or abnormally elevated in people who have no cancer at all (false positive). The main use of CA 19-9 is therefore to see whether a pancreatic tumor is secreting it; if that is the case, then the levels should fall when the tumor is treated, and they may rise again if the disease recurs.

In people with pancreatic masses, CA 19-9 can be useful in distinguishing between cancer and other diseases of the gland.