A pilot study of pretreatment [68Ga]Ga-FAPI-04 PET/CT: correlation of imaging parameters with prognosis and FAP expression in soft tissue sarcoma

OBJECTIVES: This study was developed with the primary goal of assessing any potential correlations between [68Ga]Ga -FAPI-04 PET/CT-derived parameters and the overall and progression-free survival (OS and PFS) of patients with soft tissue sarcoma (STS). The association between sarcomatous lesional uptake and FAP immunohistochemistry (IHC) results was also examined. METHODS: Patients with a primary STS diagnosis who underwent [68Ga]Ga-FAPI-04 PET/CT were retrospectively evaluated. Basic information included age, gender, tumor size location, necrosis volume, and [68Ga]Ga-FAPI-04 PET/CT-based parameters included maximum tumor standardized uptake value (SUVmax), FAPI-avid tumor volume (FTV), and total lesion FAP expression (TLF). Prognostic outcomes were analyzed using Kaplan-Meier curves and Cox regression. Spearman's correlation was used to examine the association between [68Ga]Ga-FAPI-04 uptake and FAP expression. RESULTS: Survival analyses included 22 patients, of whom 10 underwent FAP IHC staining. A significant association was observed between FAP levels and SUVmax for these STS patients (r = 0.88, P < 0.001). In univariate analyses, FTV and TLF were both significantly correlated with OS and PFS (P < 0.05). SUVmax, in contrast, was only correlated with patient OS. FTV and TLF values were established as significant independent predictors of PFS (HR = 4.15, P = 0.01) and OS (HR = 4.12, P = 0.02). In addition, a roughly 3-fold greater risk of progression was also noted for patients with a tumor necrosis volume exceeding 50% relative to patients below this threshold. CONCLUSION: FAP expression is significantly correlated with [68Ga]Ga-FAPI-04 uptake and pre-treatment [68Ga]Ga-FAPI-04 PET/CT parameters can predict survival outcomes for STS patients. ADVANCES IN KNOWLEDGE: Clinical utility of [68Ga]Ga-FAPI-04 in STS remains unclear, and there aren't many similar studies in the literature. We evaluated the role of [68Ga]Ga-FAPI-04 in the prognosis of STS.