Precision Theranostic Approach Using Multi-tracer PET/CT Imaging and PSMA-Based Targeted Radionuclide Therapy in Metastatic Synovial Sarcoma

Synovial sarcomas are a relatively uncommon subtype of soft tissue sarcomas, usually treated with surgical excision followed by chemo-radiation therapy. Herein, an interesting report of a 32-year-old male, a case of metastatic synovial sarcoma diagnosed 6 years ago and developed multiple treatment failures, is illustrated. Triple positron emission tomography/computed tomography (PET/CT) modalities were utilized, encompassing [18F]FDG, [68Ga]Ga-FAPI-04, and [68Ga]Ga PSMA-11 radiotracers. Despite extensive treatments (systemic multi-lines chemotherapy, molecular targeted therapy and radiotherapy), the patient demonstrated a progressive and highly [18F]F-FDG-avid disease and low fibroblast activation protein inhibitor (FAPI) tracer uptake on [18F]F-FDG PET/CT and [68Ga]Ga-FAPI-04 PET/CT, respectively, with comparatively high prostate-specific membrane antigen (PSMA) uptake in metastatic lung lesions on [68Ga]Ga-PSMA-11 PET/CT. Subsequently, the patient was considered for PSMA-based targeted radionuclide therapy (TRT) as a precision treatment approach. The case demonstrates the imperative role of multi-tracer PET/CT imaging, PSMA avidity, and the possibility of PSMA-TRT theranostics in metastatic synovial sarcomas.