DFSP — SCE Dermatology MCQ

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A 55-year-old man has a dermatofibrosarcoma protuberans (DFSP) on his trunk. Histology shows a spindle cell tumour with storiform pattern, positive for CD34 and negative for Factor XIIIa. What is the characteristic genetic abnormality?

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Correct answer: D — t(17;22) translocation producing COL1A1-PDGFB fusion gene

The correct answer is D, t(17;22) translocation producing COL1A1-PDGFB fusion gene. DFSP is a locally infiltrative dermal sarcoma in which the reciprocal translocation between chromosomes 17 and 22 fuses the collagen 1 alpha 1 gene to platelet derived growth factor B, producing a chimeric protein that drives constitutive PDGF receptor beta activation and an autocrine growth loop. This molecular signature underlies the storiform spindle cell histology and the CD34 positive, Factor XIIIa negative immunoprofile described, which is the reverse of the pattern seen in dermatofibroma. Detection of this fusion (by FISH or RT-PCR) is diagnostically confirmatory in equivocal cases and is exploited therapeutically: imatinib, a PDGFR tyrosine kinase inhibitor, is active in locally advanced, recurrent or metastatic DFSP harbouring this rearrangement. Surgical excision with wide margins or Mohs surgery remains first line for localised disease, but this fusion is what defines DFSP pathogenetically among spindle cell dermal tumours.

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/skin-conditions