CA19-9

CA19-9 (carbohydrate antigen 19-9 or sialylated Lewis (a) antigen) is a blood test from the tumor marker category. [MeshName|CA-19-9+Antigen|x] It was discovered in patients with colon cancer and pancreatic cancer in 1981.cite journal |author=Koprowski H, Herlyn M, Steplewski Z, Sears HF |title=Specific antigen in serum of patients with colon carcinoma |journal=Science |volume=212 |issue=4490 |pages=53–5 |year=1981 |pmid=6163212 |doi=10.1126/science.6163212] Increased levels of CA19-9 are also found in non-malignant conditions, such as Mirizzi's syndrome and diseases of the bile ducts and liver. [cite journal |author=Robertson A, Davidson B |title=Mirizzi syndrome complicating an anomalous biliary tract: a novel cause of a hugely elevated CA19-9 |journal=European journal of gastroenterology & hepatology |volume=19 |issue=2 |pages=167–9 |year=2007 |pmid=17273004 |doi=10.1097/MEG.0b013e3280122879]

Guidelines from the American Society of Clinical Oncology discourage the use of CA19-9 as a 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 CA19-9 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.cite journal |author=Locker G, Hamilton S, Harris J, Jessup J, Kemeny N, Macdonald J, Somerfield M, Hayes D, Bast R |title=ASCO 2006 update of recommendations for the use of tumor markers in gastrointestinal cancer |journal=J. Clin. Oncol. |volume=24 |issue=33 |pages=5313–27 |year=2006 |pmid=17060676|url=http://jco.ascopubs.org/cgi/content/full/24/33/5313 |doi=10.1200/JCO.2006.08.2644]

In patients who lack the Lewis antigen (a blood type protein on red blood cells), which is about 5% of the population, CA19-9 is not elevated in pancreatic cancer even with large tumors because they have a deficiency of a fucosyltransferase enzyme that is needed to produce CA19-9 as well as the Lewis antigen.

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