Skin tumours: desmoplastic melanoma: 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: desmoplastic melanoma

Sample item

A 72-year-old has a scar-like, firm, amelanotic plaque on the sun-damaged cheek that recurred locally after excision. Histology shows spindle cells in a fibrous stroma with neurotropism and strong S100 positivity, but HMB-45 and Melan-A are negative. What is the diagnosis?

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

The answer and the reasoning

B. Desmoplastic melanoma

Desmoplastic melanoma is a spindle-cell melanoma in sun-damaged skin of older people, often amelanotic and neurotropic, with high local recurrence. It is typically S100 and SOX10 positive but often negative for HMB-45 and Melan-A. Wide excision and sometimes adjuvant radiotherapy are used.

Option by option

  • A. Leiomyosarcoma

    Leiomyosarcoma is positive for smooth muscle markers such as desmin and actin and negative for S100.

  • B. Desmoplastic melanoma (correct)

    Correct. S100-positive neurotropic spindle cells in sun-damaged skin define desmoplastic melanoma.

  • C. Dermatofibrosarcoma protuberans

    Dermatofibrosarcoma protuberans is CD34 positive and S100 negative with a storiform pattern.

  • D. Scar fibrosis

    Scar fibrosis would not show atypical spindle cells staining for S100.

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 B, Desmoplastic melanoma. Desmoplastic melanoma is a spindle-cell melanoma in sun-damaged skin of older people, often amelanotic and neurotropic, with high local recurrence.

Why is "Leiomyosarcoma" not the answer?

Leiomyosarcoma is positive for smooth muscle markers such as desmin and actin and negative for S100.

Why is "Dermatofibrosarcoma protuberans" not the answer?

Dermatofibrosarcoma protuberans is CD34 positive and S100 negative with a storiform pattern.

Why is "Scar fibrosis" not the answer?

Scar fibrosis would not show atypical spindle cells staining for S100.

What concept does this question test?

It tests Skin tumours: desmoplastic melanoma in Dermatology. It is typically S100 and SOX10 positive but often negative for HMB-45 and Melan-A. Wide excision and sometimes adjuvant radiotherapy are used.

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: desmoplastic melanoma?

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.