CA 19-9 as a serum biomarker in cancer

Serum biomarkers in cancer diagnosis or prognosis continue to be part of an evolving field and have been a promising noninvasive tool that may aid in the diagnosis and monitoring of disease in a number of different cancers. Serum carbohydrate antigen 19-9 (CA19-9) is a biomarker that found utilitymainly in biliary tract and pancreatic malignancies as a prognostic marker in monitoring response to treatment and as an indication of disease recurrence. Unfortunately, CA 19-9 levels may lack specificity given that other cancers originating from the ovaries, stomach, colon, and lung may be associated with elevated levels. There are also many benign conditions that are associated with higher levels of CA 19-9. The antigen was discovered in the 1970s and has been studied extensively in various malignancies to validate its utility as a screening, prognostic, or diagnostic tool. CA 19-9 has been used most commonly as a biomarker in pancreatic cancer as a prognostic and predictive tool and less commonly in other malignancies. This chapter will focus mainly on utility of CA 19-9 in pancreatic cancer and biliary tract cancers.