Neoplasia: carcinoma of unknown primary: practice question

A Pathology 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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Pathology · Neoplasia: carcinoma of unknown primary

Sample item

A 62-year-old man has multiple liver metastases from adenocarcinoma with no known primary. Tumour cells are CK20 positive, CK7 negative and CDX2 positive, and TTF-1 negative. Which primary site is most likely?

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

The answer and the reasoning

D. Colorectum

A CK20-positive, CK7-negative, CDX2-positive profile indicates intestinal differentiation, most often colorectal adenocarcinoma. Lung adenocarcinoma is usually CK7 and TTF-1 positive, and breast and ovarian serous tumours are CK7 positive and CK20 negative.

Option by option

  • A. Breast

    Breast carcinoma is usually CK7 positive and CK20 negative, with GATA3 expression.

  • B. Lung

    Lung adenocarcinoma is typically CK7 and TTF-1 positive, which is excluded here.

  • C. Ovary

    Serous ovarian carcinoma is CK7 positive and CK20 negative.

  • D. Colorectum (correct)

    Correct. CK20 with CDX2 and absent CK7 is the usual colorectal profile.

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.

More Pathology questions

Questions about this Pathology question

What is the answer to this Pathology question?

The best answer is D, Colorectum. A CK20-positive, CK7-negative, CDX2-positive profile indicates intestinal differentiation, most often colorectal adenocarcinoma.

Why is "Breast" not the answer?

Breast carcinoma is usually CK7 positive and CK20 negative, with GATA3 expression.

Why is "Lung" not the answer?

Lung adenocarcinoma is typically CK7 and TTF-1 positive, which is excluded here.

Why is "Ovary" not the answer?

Serous ovarian carcinoma is CK7 positive and CK20 negative.

What concept does this question test?

It tests Neoplasia: carcinoma of unknown primary in Pathology. Lung adenocarcinoma is usually CK7 and TTF-1 positive, and breast and ovarian serous tumours are CK7 positive and CK20 negative.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Neoplasia: carcinoma of unknown primary?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.