EWSR1 and alveolar rhabdomyosarcoma: We found that PPTC PDX models largely maintain known oncogenic driver fusions specific to their histologies: all alveolar rhabdomyosarcoma models harbored PAX3-FOXO1 fusions, all Ewing sarcoma samples with RNA-seq data showed EWSR1-FLI1 fusions, all Ph+ ALL tumors contained BCR-ABL1 fusions, and KMT2A (MLL) fusions were detected in all MLL-ALL models (Table S5).