To validate expression of various ECM proteins upregulated in TAZ-CAMTA1 and YAP-TFE3 expressing cells (Figure 3—source data 2), we performed immunohistochemistry for COL1A1 (Collagen type I alpha one chain), CTGF (Connective tissue growth factor), VTN (vitronectin), and FBLN5 (Fibulin-5) on EHE clinical samples and compared expression with two histological mimics of EHE, epithelioid angiosarcoma (E-AS) and epithelioid hemangioma (EH). This evidence concerns the gene YAP1 and epithelioid hemangioendothelioma.