Neoplasia: tumour immunity and checkpoint inhibitors: 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: tumour immunity and checkpoint inhibitors

Sample item

A 62-year-old man with metastatic melanoma receives pembrolizumab. After 8 weeks he has watery diarrhoea, and colonoscopy shows diffuse colonic inflammation. What is the mechanism of this adverse effect?

ATumour lysis products damaging the colonic mucosaBLoss of PD-1-mediated T cell inhibition leads to autoimmune inflammationCSerotonin release from enterochromaffin cell hyperplasiaDDirect cytotoxic injury to dividing crypt epithelial cells

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

The answer and the reasoning

B. Loss of PD-1-mediated T cell inhibition leads to autoimmune inflammation

Pembrolizumab blocks the PD-1 receptor on T cells, releasing a physiological brake on immune activation. The resulting immune-related adverse events include colitis, hepatitis, pneumonitis, thyroiditis and hypophysitis, treated with corticosteroids and sometimes infliximab.

Option by option

A. Tumour lysis products damaging the colonic mucosa
Tumour lysis syndrome causes metabolic derangement and renal injury, not colitis.
B. Loss of PD-1-mediated T cell inhibition leads to autoimmune inflammation (correct)
Removal of a checkpoint brake allows self-reactive T cells to attack normal tissue such as the colon.
C. Serotonin release from enterochromaffin cell hyperplasia
Serotonin release is the basis of carcinoid syndrome and is not an effect of checkpoint inhibitors.
D. Direct cytotoxic injury to dividing crypt epithelial cells
Direct injury to crypt cells describes the mechanism of cytotoxic chemotherapy.

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 Pathology question

What is the answer to this Pathology question?

The best answer is B, Loss of PD-1-mediated T cell inhibition leads to autoimmune inflammation. Pembrolizumab blocks the PD-1 receptor on T cells, releasing a physiological brake on immune activation.

Why is "Tumour lysis products damaging the colonic mucosa" not the answer?

Tumour lysis syndrome causes metabolic derangement and renal injury, not colitis.

Why is "Serotonin release from enterochromaffin cell hyperplasia" not the answer?

Serotonin release is the basis of carcinoid syndrome and is not an effect of checkpoint inhibitors.

Why is "Direct cytotoxic injury to dividing crypt epithelial cells" not the answer?

Direct injury to crypt cells describes the mechanism of cytotoxic chemotherapy.

What concept does this question test?

It tests Neoplasia: tumour immunity and checkpoint inhibitors in Pathology. The resulting immune-related adverse events include colitis, hepatitis, pneumonitis, thyroiditis and hypophysitis, treated with corticosteroids and sometimes infliximab.

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 Neoplasia: tumour immunity and checkpoint inhibitors?

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.