Diagnostic value of Ga-68 FAPI PET imaging in patients with sarcoma

Aim: This study aimed to evaluate the diagnostic performance of Ga-68 FAPI PET compared to F-18 FDG PET in patients with histologically confirmed sarcoma. Materials and Methods: Thirty sarcoma patients who previously underwent FDG PET were prospectively enrolled and imaged with Ga-68 FAPI-04 PET. PET images were visually assessed by three independent readers for lesion detection and localization. Semi-quantitative analysis of tracer uptake was also performed. Histopathology and follow-up imaging served as reference standards. Sensitivity, specificity, positive predictive value (PPV), and accuracy were calculated for both modalities on lesion- and patient-based analyses. Results: Lesion-based analysis showed that FAPI PET detected more true positive lesions, particularly in bone and lung metastases, where its sensitivity was higher than FDG PET. Although FDG PET had higher specificity, the difference was not considered meaningful. In patient-based analysis, both modalities showed high sensitivity, PPV and accuracy. Mean SUVmax, SUVmax of the primary tumor, SUVmean, and SULpeak, as well as tumor-to-background ratios (TBR) with liver and blood pool, were significantly higher in FAPI PET compared to FDG PET. Across subgroups with low, high, or undefined tumor grade, FAPI PET demonstrated higher SUVmax values than FDG PET, most notably in low-grade sarcomas. Inter-reader agreement for FAPI PET was excellent. Conclusion: FAPI PET showed higher sensitivity than FDG PET in sarcoma patients. Intense FAPI uptake was observed in both low- and high-grade tumors, including those where FDG PET is known to be less sensitive. These findings support its potential role in theranostics.