Pancreas: carcinoma tumour marker: practice question

A General Surgery question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Surgery · Pancreas: carcinoma tumour marker

Sample item

A 62-year-old man has painless jaundice and a 3 cm pancreatic head mass on CT. Biopsy confirms ductal adenocarcinoma, yet serum CA 19-9 is undetectable. What is the likeliest explanation?

AHe is Lewis antigen negative and cannot synthesise CA 19-9BObstructive jaundice lowers CA 19-9 levelsCThe tumour is a neuroendocrine tumourDThe assay is invalid below a bilirubin of 10 mg/dL

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. He is Lewis antigen negative and cannot synthesise CA 19-9

CA 19-9 is the sialylated Lewis-a antigen. About 5 to 10% of the population is Lewis a-negative, b-negative and cannot produce it, so the test is falsely negative even in advanced cancer. Conversely, biliary obstruction and cholangitis can falsely raise it, so it is best used for follow-up and not for screening.

Option by option

A. He is Lewis antigen negative and cannot synthesise CA 19-9 (correct)
Correct. Lewis-negative individuals do not make CA 19-9, so levels stay undetectable.
B. Obstructive jaundice lowers CA 19-9 levels
Biliary obstruction raises CA 19-9 and does not lower it.
C. The tumour is a neuroendocrine tumour
Biopsy proved ductal adenocarcinoma, which is not a neuroendocrine tumour.
D. The assay is invalid below a bilirubin of 10 mg/dL
No bilirubin threshold invalidates the assay in this way.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this General Surgery question

What is the answer to this General Surgery question?

The best answer is A, He is Lewis antigen negative and cannot synthesise CA 19-9. CA 19-9 is the sialylated Lewis-a antigen.

Why is "Obstructive jaundice lowers CA 19-9 levels" not the answer?

Biliary obstruction raises CA 19-9 and does not lower it.

Why is "The tumour is a neuroendocrine tumour" not the answer?

Biopsy proved ductal adenocarcinoma, which is not a neuroendocrine tumour.

Why is "The assay is invalid below a bilirubin of 10 mg/dL" not the answer?

No bilirubin threshold invalidates the assay in this way.

What concept does this question test?

It tests Pancreas: carcinoma tumour marker in General Surgery. About 5 to 10% of the population is Lewis a-negative, b-negative and cannot produce it, so the test is falsely negative even in advanced cancer. Conversely, biliary obstruction and cholangitis can falsely raise it, so it is best used for follow-up and not for screening.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Pancreas: carcinoma tumour marker?

Learn classic signs and eponyms alongside what they diagnose. Then use the flashcards and the other General Surgery questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.