CA 19-9

Carbohydrate antigen 19-9 (CA19-9) measures the circulating levels of a carbohydrate molecule known as Sialyl LewisA. This molecule is normally found on the surface of cells and aids in cellular communications and recognition. About 5% of the population lack the genes required for generation of Sialyl Lewis A and do not make this carbohydrate.
CA19-9 levels are usually elevated in pancreatic and biliary malignancies, but can also rise in oesophageal, hepatic or colon cancers.

Use in Screening

Several large studies in asymptomatic populations have been done (Satake et al (1994), Kim et al (2004) and Chang et al (2006)). In general, although CA 19-9 has close to 100% sensitivity for pancreatic cancer, the false positive rate is very high and the positive predictive value is only 0.5-0.9% (ie. only 1/1000 asymptomatic patients with an elevated CA 19-9 will have pancreatic cancer), and in most cases 'early' diagnosis does not convey operability.
Therefore, CA 19-9 alone is not a useful screening test for pancreatic cancer as it does not fulfil the WHO requirements of an effective screening test.

Use in Diagnosis

In patients with a pancreatic mass, an elevated CA 19-9 in combination with other evidence of malignancy (eg. weight loss) is a very sensitive predictor for pancreatic cancer. Elevated CA 19-9 is a poor prognostic factor but does not independently influence the resectability of a particular pancreatic cancer.

Use in Disease Monitoring

Post-operatively, the presence of an elevated CA 19-9 is associated with a high risk of metastatic disease and early disease recurrence.
In patients receiving systemic therapy, CA 19-9 (if elevated) provides good concordance with treatment effect. A falling CA 19-9 in combination with systemic therapy predicts for improved survival.