Comparable Diagnostic Performance of 68 Ga-FAPI and 18 F-FDG PET/CT in Perineal Rhabdomyosarcoma.

A 14-year-old boy with inguinal lymphadenopathy and scrotal swelling was diagnosed with perineal rhabdomyosarcoma (RMS) via lymph node biopsy. Initial staging with 18 F-FDG PET/CT revealed hypermetabolic lymph nodes and a perineal mass overlooked on contrast-enhanced CT assessment. A complementary 68 Ga-FAPI-46 PET/CT scan demonstrated comparable lesion detection with higher target-to-background contrast in the primary tumor located in the perineum. This case highlights the diagnostic value of FAP-targeted imaging in pediatric RMS and supports its potential theranostic role in soft tissue sarcomas, expanding current understanding of FAPI avidity in this rare tumor subtype.