A locus-specific loss of heterozygosity in the PEComa but not in the sinonasal carcinoma was identified, suggesting the causative role of the splice mutation in the PEComa pathogenesis, because we excluded known pathogenetic pathways characteristic to PEComas (<i>TSC1/2</i>, <i>TFE3</i>, <i>RAD51B</i>). This evidence concerns the gene TSC1 and neoplasm with perivascular epithelioid cell differentiation.