L1CAM and rhabdomyosarcoma: Here, we report the case of a 13-year-old adolescent boy with relapsed and refractory rhabdomyosarcoma who developed early hyperprogression 3 weeks after CAR-T treatment (target: B7H3 and CD171), which was detected by fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/computed tomography (CT).