Cancer Antigen 19-9 (CA 19-9)

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Subject: Cancer Antigen 19-9 (CA 19-9)

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Definition

  • 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.

 
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