Early Hyperprogression of Rhabdomyosarcoma Detected by ¹⁸ F-FDG PET/CT Three Weeks after CAR-T Treatment

Chimeric antigen receptor T-cell (CAR-T) treatment has been widely used in the treatment of hematological malignancies, and its application has been gradually expanded to the research and treatment of solid tumors. However, unconventional types of response may occur after CAR-T treatment, such as hyperprogression, resulting in terrible outcomes. 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 ( ¹⁸ F-FDG) positron emission tomography (PET)/computed tomography (CT). The patient eventually underwent amputation. Attention should be paid to the possibility of early hyperprogression after CAR-T treatment, and ¹⁸ F-FDG PET/CT has an absolute advantage in early evaluating treatment response to immunotherapy.