CA 19-9
CA 19-9 and Cancer — Tumor Burden Marker, Treatment Monitoring Tool, and Its Limits
CA 19-9 (also known as sialyl-Lewis A) is a glycan epitope expressed on mucins and other glycoproteins. It is not a gene and not a cancer-specific molecule by design.
Typically UPREGULATED in circulation in certain cancers due to increased production and/or impaired biliary clearance.
Elevation reflects tumor burden and ductal involvement, not oncogenic signaling.
Where CA 19-9 Is Clinically Relevant
Highest utility:
-Pancreatic ductal adenocarcinoma (PDAC)
-Cholangiocarcinoma
-Gallbladder cancer
Secondary/limited utility:
-Gastric and colorectal cancers (subset; nonspecific)
Appropriate uses
-Baseline assessment at diagnosis (prognostic)
-Monitoring response to therapy
-Detecting recurrence after treatment
-Trend analysis over time (most important)
CA 19-9 can be elevated without cancer, especially with:
-Biliary obstruction or cholestasis
-Cholangitis or pancreatitis
-Liver disease
The Lewis Antigen Issue (Often Missed)
~5–10% of people are Lewis antigen–negative (Leᵃ⁻ᵇ⁻) and cannot synthesize CA 19-9.
Implications:
-CA 19-9 may be falsely low or undetectable despite advanced cancer
-A “normal” CA 19-9 does not exclude disease in these patients
Higher baseline CA 19-9 → worse prognosis (on average)
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