What is the role of carbohydrate antigen 19-9 testing in the evaluation of pancreatic cancer?

Updated: Oct 02, 2020
  • Author: Tomislav Dragovich, MD, PhD; Chief Editor: N Joseph Espat, MD, MS, FACS  more...
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The CA 19-9 antigen is a sialylated oligosaccharide that is most commonly found on circulating mucins in cancer patients. [44] It is also normally present within the cells of the biliary tract and can be elevated in acute or chronic biliary disease. Some 5-10% of patients lack the enzyme necessary to produce CA 19-9; in these patients with low or absent titer of CA 19-9, monitoring disease with this tumor marker will not be possible.

The reference range of CA 19-9 is less than 33-37 U/mL in most laboratories. Of patients with pancreatic carcinoma, 75-85% have elevated CA 19-9 levels. In the absence of biliary obstruction, intrinsic liver disease, or benign pancreatic disease, a CA 19-9 value of greater than 100 U/mL is highly specific for malignancy, usually pancreatic.

Evaluation of CA 19-9 levels has been used as an adjunct to imaging studies for helping to determine the resectability potential of pancreatic carcinoma. Fewer than 4% of patients with a CA 19-9 level of more than 300 U/mL have been found to have resectable tumors.

Unfortunately, CA 19-9 is least sensitive for small, early stage pancreatic carcinomas and thus has not proven to be effective for the early detection of pancreatic cancer or as a screening tool. [44]

An elevated CA 19-9 level is found in 0.2% of an asymptomatic population older than 40 years. Of these elevations, 80% are false-positive results. If only symptomatic patients are studied, 4.3% have elevated CA 19-9 levels. Two thirds of these results are false positive.

Although no standardized role has been set for CA 19-9 in the diagnosis of pancreatic carcinoma, it has growing importance in the staging and follow-up of patients with this disease. Patients presenting with low levels of CA 19-9 (< 100 IU) are unlikely to have occult metastatic disease and therefore may not need a staging laparoscopy prior to resection if other imaging shows no advanced disease.

Additionally, during surgical, chemotherapeutic, and/or radiotherapeutic treatment for pancreatic cancer, a falling CA 19-9 seems to be a useful surrogate finding for clinical response to the therapy. If biliary obstruction is not present, a rising CA 19-9 suggests progressive disease.

Preoperative CA 19-9 levels may be of prognostic value, with high levels indicating poorer outcome and less chance of resectability. [45, 46] Preoperative values above 50 U/mL have been shown to be associated with higher chances of recurrence.

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