Skin tumours: ultraviolet carcinogenesis: practice question

A Dermatology 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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Dermatology · Skin tumours: ultraviolet carcinogenesis

Sample item

Chronic sun exposure is the main cause of cutaneous squamous cell carcinoma. Which DNA lesion is the characteristic signature of UV damage?

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

The answer and the reasoning

C. Cyclobutane pyrimidine dimers causing C to T and CC to TT mutations

UVB is absorbed by DNA and forms cyclobutane pyrimidine dimers and 6-4 photoproducts between adjacent pyrimidines. If unrepaired, they produce C to T and CC to TT signature mutations, often in TP53. Nucleotide excision repair removes them, which is why it is defective in xeroderma pigmentosum.

Option by option

  • A. Oxidised guanine causing G to T changes

    Oxidised guanine arises from reactive oxygen species and gives G to T changes.

  • B. Interstrand crosslinks caused by alkylating agents

    Interstrand crosslinks are typical of alkylating agents and cisplatin.

  • C. Cyclobutane pyrimidine dimers causing C to T and CC to TT mutations (correct)

    Correct. Pyrimidine dimers and the resulting C to T and CC to TT mutations are the UV signature.

  • D. Double strand breaks from ionizing radiation

    Double strand breaks are typical of ionizing radiation.

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 Dermatology questions

Questions about this Dermatology question

What is the answer to this Dermatology question?

The best answer is C, Cyclobutane pyrimidine dimers causing C to T and CC to TT mutations. UVB is absorbed by DNA and forms cyclobutane pyrimidine dimers and 6-4 photoproducts between adjacent pyrimidines.

Why is "Oxidised guanine causing G to T changes" not the answer?

Oxidised guanine arises from reactive oxygen species and gives G to T changes.

Why is "Interstrand crosslinks caused by alkylating agents" not the answer?

Interstrand crosslinks are typical of alkylating agents and cisplatin.

Why is "Double strand breaks from ionizing radiation" not the answer?

Double strand breaks are typical of ionizing radiation.

What concept does this question test?

It tests Skin tumours: ultraviolet carcinogenesis in Dermatology. If unrepaired, they produce C to T and CC to TT signature mutations, often in TP53. Nucleotide excision repair removes them, which is why it is defective in xeroderma pigmentosum.

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 Skin tumours: ultraviolet carcinogenesis?

Learn each condition by its primary lesion, site and signature sign. Then use the flashcards and the other Dermatology 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.