Cancer Antigen 19-9 (CA 19-9)

CA 19-9 is a modified Lewis(a) blood group antigen and has been used as a tumor marker. It is shown to be elevated in sera of some patients with GI tumors.

Normal value: <35 U/mL.

Use

Detection, diagnosis, and prognosis of pancreatic cancer

Monitor response to therapy (e.g., postsurgical recurrence correlates with increased concentrations)

May be a useful adjunct to CEA for diagnosis and to detect early recurrence of certain cancers

May indicate development of cholangiocarcinoma in patients with primary sclerosing cholangitis

Interpretation

Increased In

Carcinoma of the pancreas (80%).

Pancreatitis " ”concentrations are usually <75 U/mL but are much higher in pancreatic cancer.

Hepatobiliary cancer (22 " “51%).

Gastric cancer (42%).

Colon cancer (20%) is associated with very poor prognosis.

Noncancerous conditions that may elevate include cirrhosis, cholangitis, hepatitis, pancreatitis, and nonmalignant GI diseases.

Can be considered as a marker of MTC dedifferentiation and diseases aggressiveness.

Decreased In

Limitations

Individuals with blood group antigen Le a-b- do not synthesize CA 19-9 (5 " “10% of population).

No value in screening because its PPV <1%. However, levels of >1,000 U/mL have 97% PPV.

The CA 19-9 levels in a given specimen determined with assays from different manufacturers can vary due to differences in assay methods and reagent specificity and cannot be used interchangeably. If, in the course of monitoring a patient, the assay method used is changed, additional sequential testing should be carried out to confirm baseline values.