Evaluation of FAPI PET imaging in gastric cancer: a systematic review and meta-analysis

Purpose: Recent studies suggest that ⁶⁸Ga-FAPI PET/CT demonstrated superiority over ¹⁸F-FDG PET/CT in the evaluation of various cancer types, especially in gastric cancer (GC). By comprehensively reviewing and analysing the differences between ⁶⁸Ga-FAPI and ¹⁸F-FDG in GC, some evidence is provided to foster the broader clinical application of FAPI PET imaging. Methods: In this review, studies published up to July 3, 2023, that employed radionuclide labelled FAPI as a diagnostic radiotracer for PET in GC were analysed. These studies were sourced from both the PubMed and Web of Science databases. Our statistical analysis involved a bivariate meta-analysis of the diagnostic data and a meta-analysis of the quantitative metrics. These were performed using R language. Results: The meta-analysis included 14 studies, with 527 patients, of which 358 were diagnosed with GC. Overall, ⁶⁸Ga-FAPI showed higher pooled sensitivity (0.84 [95% CI 0.67-0.94] vs. 0.46 [95% CI 0.32-0.60]), specificity (0.91 [95% CI 0.76-0.98] vs. 0.88 [95% CI 0.74-0.96]) and area under the curve (AUC) (0.92 [95% CI 0.77-0.98] vs. 0.52 [95% CI 0.38-0.86]) than ¹⁸F-FDG. The evidence showed superior pooled sensitivities of ⁶⁸Ga-FAPI PET over ¹⁸F-FDG for primary tumours, local recurrence, lymph node metastases, distant metastases, and peritoneal metastases. Furthermore, ⁶⁸Ga-FAPI PET provided higher maximum standardized uptake value (SUVmax) and tumour-to-background ratios (TBR). For bone metastases, while ⁶⁸Ga-FAPI PET demonstrated slightly lower patient-based pooled sensitivity (0.93 vs. 1.00), it significantly outperformed ¹⁸F-FDG in the lesion-based analysis (0.95 vs. 0.65). However, SUVmax (mean difference [MD] 1.79 [95% CI -3.87-7.45]) and TBR (MD 5.01 [95% CI -0.78-10.80]) of bone metastases showed no significant difference between ⁶⁸Ga-FAPI PET/CT and ¹⁸F-FDG PET/CT. Conclusion: Compared with ¹⁸F-FDG, ⁶⁸Ga-FAPI PET imaging showed improved diagnostic accuracy in the evaluation of GC. It can be effectively applied to the early diagnosis, initial staging, and detection of recurrence/metastases of GC. ⁶⁸Ga-FAPI may have the potential of replacing ¹⁸F-FDG in GC in future applications.