PEComa with ASPSCR1::TFE3 fusion: expanding the molecular genetic spectrum of TFE3‐rearranged PEComa with an emphasis on overlap with alveolar soft part sarcoma

Aims Mesenchymal neoplasms involving TFE3 gene fusions are diverse, mainly include alveolar soft part sarcoma (ASPS) that is characterised by ASPSCR1 :: TFE3 fusion, and a small subset of perivascular epithelioid cell tumours (PEComas) referred to as TFE3 ‐rearranged PEComa, that most frequently harbours SFPQ :: TFE3 fusion. Historically, ASPS and TFE3 ‐rearranged PEComa are considered two distinctive entities despite their known morphological overlap. However, recent studies have suggested a potential histogenetic relationship between them, and several neoplasms that showed morphological features more closely fit PEComa rather than ASPS but harboured ASPSCR1 :: TFE3 fusion have been documented. In this study, we report three cases of PEComa with ASPSCR1 :: TFE3 fusion. Methods and results Clinicopathological features were assessed and partner agnostic targeted next‐generation sequencing on clinically validated platforms were performed. The patients are two females and one male with age at presentation ranging from 21 to 51 years. All three tumours were located in the viscera (rectum, kidney and cervix). On a relatively limited follow‐up period (range = 9–15 months), all patients are alive without evidence of recurrent or metastatic disease. The neoplasms were composed of tight nested architecture of epithelioid clear cells separated by a delicate vascular network, two of which were associated with sheets of plump spindle cells, and none showed significant discohesive tumour morphology. Immunohistochemically, in addition to TFE3 protein, all three neoplasms demonstrated co‐expression of melan‐A and smooth muscle actin. RNA‐sequencing identified ASPSCR1 :: TFE3 fusion in all three cases that were confirmed by subsequent fluorescence in ‐ situ hybridisation analyses. Conclusions Our study expands the molecular genetic spectrum of TFE3 ‐rearranged PEComa and further indicates its close relationship to ASPS.