A 60-year-old man presents with obstructive jaundice and a pancreatic head mass on imaging. CA 19-9 is elevated at 850 U/mL. Which statement about CA 19-9 is MOST accurate?

• A CA 19-9 is elevated only in pancreatic adenocarcinoma and has no false positives
• B CA 19-9 is the tumor marker of choice for screening hepatocellular carcinoma
• C CA 19-9 is a transcription factor that drives pancreatic cancer proliferation
• D CA 19-9 requires the Lewis antigen to be expressed; Lewis-negative individuals cannot produce it ✓

Explanation

CA 19-9 is a sialylated Lewis blood group antigen. Approximately 5-10% of individuals are Lewis-negative (Lea-b-) and cannot synthesize CA 19-9 regardless of tumor burden. Option A is false because CA 19-9 can be elevated in cholangitis, cholangiocarcinoma, and other GI malignancies. Option C is wrong; CA 19-9 is a carbohydrate antigen, not a transcription factor. Option B describes AFP, not CA 19-9.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.