ATF1 and synovial sarcoma: To further investigate the effect of PI3K inhibitors in a wide variety of TRS subtypes, we exploited a series of patient-derived tumor cells (PDCs) originally established from surgical tumor specimens of various origins including SS, ES, ASPS, clear cell sarcoma (CCS, harboring the EWSR1-ATF1 fusion gene), CIC-DUX4 sarcoma (CDS, harboring the CIC-DUX4 fusion gene) and Dermatofibrosarcoma protuberans (DFSP, harboring the COL1A1-PDGFB fusion gene).