In general, fusion-driven neoplasms, including JAZF1-rearranged LG-ESS, YWHAE- or BCOR-altered HG-ESS, ALK- or NTRK-rearranged IMTs, and TFE3-rearranged PEComas, harbor early, lineage-defining genomic events that are consistently detectable across disease stages. The gene discussed is TFE3; the disease is neoplasm with perivascular epithelioid cell differentiation.