Prognostic Implications of ⁶⁸Ga-FAPI-46 PET/CT-Derived Parameters on Overall Survival in Various Types of Solid Tumors

Tumoral fibroblast activation protein expression is associated with proliferation and angiogenesis and can be visualized by PET/CT. We examined the prognostic value of [⁶⁸Ga]Ga-fibroblast activation protein inhibitor (FAPI) (⁶⁸Ga-FAPI)-46 PET/CT for different tumor entities in patients enrolled in 2 prospective imaging studies (NCT05160051, n = 30; NCT04571086, n = 115). Methods: Within 4 wk, 145 patients underwent ⁶⁸Ga-FAPI-46 and [¹⁸F]FDG (¹⁸F-FDG) PET/CT. The association between overall survival (OS) and sex, age, tumor entity, total lesion number, highest SUV_max, and the presence of each nodal, visceral, and bone metastasis was tested using univariate Cox regression analysis. Multivariate analyses were performed for prognostic factors with P values of less than 0.05. Results: In the univariate analysis, shorter OS was associated with total lesion number and the presence of nodal, visceral, and bone metastases on ⁶⁸Ga-FAPI-46 PET/CT (hazard ratio [HR], 1.06, 2.18, 1.69, and 2.05; P < 0.01, < 0.01, = 0.04, and = 0.02, respectively) and ¹⁸F-FDG PET/CT (HR, 1.05, 2.31, 1.76, and 2.30; P < 0.01, < 0.01, = 0.03, and < 0.01, respectively) and with SUV_max on ⁶⁸Ga-FAPI-46 PET/CT (HR, 1.03; P = 0.03). In the multivariate analysis, total lesion number on ⁶⁸Ga-FAPI-46 PET/CT was an independent risk factor for shorter OS (HR, 1.05; P = 0.02). In patients with pancreatic cancer, shorter OS was associated with total lesion number on ⁶⁸Ga-FAPI-46 PET/CT (HR, 1.09; P < 0.01) and bone metastases on ¹⁸F-FDG PET/CT (HR, 31.39; P < 0.01) in the univariate analysis and with total lesion number on ⁶⁸Ga-FAPI-46 PET/CT (HR, 1.07; P = 0.04) in the multivariate analyses. In breast cancer, total lesion number on ⁶⁸Ga-FAPI-46 PET/CT (HR, 1.07; P = 0.02), as well as bone metastases on ¹⁸F-FDG PET/CT (HR, 9.64; P = 0.04), was associated with shorter OS in the univariate analysis. The multivariate analysis did not reveal significant prognostic factors. In thoracic cancer (lung cancer and pleural mesothelioma), the univariate and multivariate analyses did not reveal significant prognostic factors. Conclusion: Disease extent on ⁶⁸Ga-FAPI-46 PET/CT is a predictor of short OS and may aid in future risk stratification by playing a supplemental role alongside ¹⁸F-FDG PET/CT.