Cutaneous PEComa does not harbour TFE3 gene fusions: immunohistochemical and molecular study of 17 cases

Aims The family of perivascular epithelioid cell tumours (PEComas) comprises a related group of mesenchymal tumours of uncertain origin that show both smooth muscle and melanocytic differentiation markers. TFE3 nuclear immunoreactivity may be viewed as a supporting marker, as it has been found in a subset of visceral PEComas. We immunohistochemically analysed 17 cases of primary cutaneous PEComas for TFE3, and five of them also for SOX‐10, and also analysed them by FISH for TFE3 rearrangement. Methods and results PEComas presented as skin‐coloured tumours, in 12 women and five men, with a median age of 49.5 years. Tumours showed either a mixed clear cell–epithelioid cell pattern or a monomorphous clear cell pattern. None of the primary cutaneous PEComas showed detectable TFE3 or SOX‐10 positivity. FISH assay for TFE3 rearrangement yielded negative results in all of the tested tumours. Conclusions Cutaneous PEComas are mostly composed of clear cells, and, unlike a subset of visceral and deep‐seated PEComas, cutaneous PEComas consistently lack TFE3 expression. Owing to the lack of SOX‐10 expression, a neural crest origin could not be shown.