Skin tumours: DFSP histology: 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: DFSP histology

Sample item

A firm plaque on the trunk of a young adult recurs after excision with narrow margins. Histology shows spindle cells in a storiform pattern infiltrating fat in a honeycomb manner. Which marker is expected?

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

The answer and the reasoning

A. CD34 positivity

Dermatofibrosarcoma protuberans shows storiform spindle cell growth, honeycomb fat infiltration and CD34 positivity, with COL1A1-PDGFB fusion. Wide local excision or Mohs surgery reduces recurrence. Dermatofibroma is usually CD34 negative.

Option by option

  • A. CD34 positivity (correct)

    Correct. DFSP is CD34 positive.

  • B. Cytokeratin 20 dot pattern

    Perinuclear dot CK20 is Merkel cell carcinoma.

  • C. S-100 positivity

    S-100 is positive in melanoma and neural tumours.

  • D. Desmin positivity

    Desmin marks smooth or skeletal muscle tumours.

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.

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Questions about this Dermatology question

What is the answer to this Dermatology question?

The best answer is A, CD34 positivity. Dermatofibrosarcoma protuberans shows storiform spindle cell growth, honeycomb fat infiltration and CD34 positivity, with COL1A1-PDGFB fusion.

Why is "Cytokeratin 20 dot pattern" not the answer?

Perinuclear dot CK20 is Merkel cell carcinoma.

Why is "S-100 positivity" not the answer?

S-100 is positive in melanoma and neural tumours.

Why is "Desmin positivity" not the answer?

Desmin marks smooth or skeletal muscle tumours.

What concept does this question test?

It tests Skin tumours: DFSP histology in Dermatology. Wide local excision or Mohs surgery reduces recurrence. Dermatofibroma is usually CD34 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 Skin tumours: DFSP histology?

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.