TFE3‐Altered Perivascular Epithelioid Cell Tumour (PEComa) of the Nasal Cavity With a Novel TRAF3::TFE3 Fusion—A Report of a Case Expanding the Molecular Genetic Spectrum and a Brief Literature Review on PEComas of the Head and Neck Region

Background Perivascular epithelioid cell tumours (PEComas) constitute a unique group of neoplasms with a distinctive myomelanocytic immunohistochemical phenotype and uncommonly occur in the head and neck region. We herein report the clinicopathologic features of a case of a sinonasal PEComa occurring in an 18‐year‐old male with a novel TRAF3::TFE3 fusion. Case Presentation The patient presented with an infiltrative nasal cavity tumour. Histologic examination showed a tumour composed of sheets and nests of epithelioid cells with clear to eosinophilic granular cytoplasm, round to oval nuclei, inconspicuous nucleoli and no mitotic activity. The tumour cells featured strong diffuse expression of smooth muscle actin and nuclear TFE3, with patchy expression of HMB45. Neoplastic cells showed no immune‐reactivity for Melan A. Molecular genetic analysis revealed a novel TRAF3(ex8)::TFE3(ex6) fusion. Conclusions This report contributes to the expanding molecular spectrum of TFE3 ‐altered PEComas of the head and neck region and discusses the differential diagnoses of these tumours. We further describe the evolving understanding of TFE3 ‐altered PEComas.