Prognostic Significance of Pretreatment [ 18 F]ALF-NOTA-FAPI-04 PET/CT in Patients With Recurrent Gastric Cancer Undergoing Combined PD-1 Inhibitor and Chemotherapy

Objective: This study aimed to evaluate the prognostic value of [ 18 F]ALF-NOTA-FAPI-04 PET/CT-derived parameters, including the maximum standardized uptake value (SUVmax), FAPI-avid tumor volume (FTV), and total lesion FAP expression (TLF), in patients with recurrent gastric cancer undergoing combined chemoimmunotherapy.We sought to establish a noninvasive imaging biomarker framework to optimize patient stratification and therapeutic decision-making. Materials and Methods:This retrospective cohort study analyzed 51 patients with recurrent gastric cancer who received programmed cell death protein 1 (PD-1) inhibitors combined with chemotherapy after gastrectomy.All patients underwent [ 18 F]ALF-NOTA-FAPI-04 PET/CT within 14 days of chemoimmunotherapy.Semi-quantitative parameters (SUVmax, FTV, and TLF) were derived using semi-automated tumor segmentation.The primary endpoint of this study was the assessment of the clinical efficacy of chemoimmunotherapy, categorized as a durable or nondurable clinical benefit.The secondary endpoints included progression-free survival (PFS) and overall survival (OS).In a subgroup of 16 patients who underwent sequential [ 18 F]FDG PET/CT within seven days of [ 18 F]ALF-NOTA-FAPI-04 PET/CT, tracer uptake values were compared between the two PET/CT examinations.Results: 51 patients were included.The median PFS and OS were 7 and 10 months, respectively.Durable clinical benefit (DCB) was observed in 30 patients and showed significantly lower SUVmax, FTV, and TLF values than non-DCB.TLF demonstrated the highest diagnostic accuracy for DCB (area under the receiver operating characteristic curve [AUC] = 0.80).Multivariable analysis identified TLF ≥ 188.88 SUVbw•cm 3 as an independent factor associated with PFS (hazard ratio [HR] = 7.29, P = 0.001) and FTV ≥ 44.17 cm 3 as an independent factor associated with OS (HR = 5.16, P = 0.010).In the subgroup analysis of 16 patients, semi-quantitative analysis demonstrated consistently higher values of [ 18 F]ALF-NOTA-FAPI-04-derived parameters than [ 18 F]FDG-derived parameters (all P < 0.001).Conclusion: [ 18 F]ALF-NOTA-FAPI-04 PET/CT may be a useful imaging tool for predicting clinical outcomes in patients with recurrent gastric cancer undergoing treatment with PD-1 inhibitors and chemotherapy.