All aRMS PDX maintained the PAX3::FOXO1 fusion; aggressive features like TP53 mutations ± loss of heterozygosity, FGFR4 mutations ± amplification, PIK3CA or NRAS mutations, and cell cycle alterations like CDK4 amplification or CDK2NA/B loss were present in the rhabdomyosarcoma PDX. Here, FGFR4 is linked to rhabdomyosarcoma.