Skin tumours: atypical fibroxanthoma: 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: atypical fibroxanthoma

Sample item

A 78-year-old man has a rapidly enlarging, ulcerated 1.5 cm nodule on the bald scalp. Histology shows pleomorphic spindle cells with atypical mitoses. Cytokeratin, S100, desmin and CD31 are negative. What is the diagnosis?

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

The answer and the reasoning

A. Atypical fibroxanthoma

Atypical fibroxanthoma is a superficial pleomorphic dermal tumour of sun-damaged head and neck skin in the elderly. It is a diagnosis of exclusion made after negative markers, and wide local excision is curative in most.

Option by option

  • A. Atypical fibroxanthoma (correct)

    Correct. A pleomorphic spindle cell tumour negative for the lineage markers is atypical fibroxanthoma.

  • B. Angiosarcoma

    Angiosarcoma would stain for CD31 and typically appears as bruise-like scalp patches.

  • C. Amelanotic melanoma

    Amelanotic melanoma would stain for S100.

  • D. Spindle cell squamous carcinoma

    Spindle cell squamous carcinoma would stain for cytokeratin or p63.

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, Atypical fibroxanthoma. Atypical fibroxanthoma is a superficial pleomorphic dermal tumour of sun-damaged head and neck skin in the elderly.

Why is "Angiosarcoma" not the answer?

Angiosarcoma would stain for CD31 and typically appears as bruise-like scalp patches.

Why is "Amelanotic melanoma" not the answer?

Amelanotic melanoma would stain for S100.

Why is "Spindle cell squamous carcinoma" not the answer?

Spindle cell squamous carcinoma would stain for cytokeratin or p63.

What concept does this question test?

It tests Skin tumours: atypical fibroxanthoma in Dermatology. It is a diagnosis of exclusion made after negative markers, and wide local excision is curative in most.

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: atypical fibroxanthoma?

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.