Comparison of [(68) Ga]Ga-FAPI-04 and [F-18]-FDG for the detection of primary and metastatic lesions in patients with gastric cancer: a bicentric retrospective study

Introduction The low sensitivity of [F-18]-fluorodeoxyglucose ([F-18]-FDG) for the diagnosis of gastric cancer limits its application. In this study, we aimed to investigate the potential advantage of [(68) Ga]Ga-FAPI-04 over [F-18]-FDG in the evaluation of gastric cancer. Methods This was a bicentric retrospective analysis of a prospective parent study (clinical trial: HS-KY-2020-826 (Huashan Hospital) and DF-2020-102 (Shanghai East Hospital)). Thirty-eight patients with gastric cancer (31 with adenocarcinoma and 7 with signet ring cell carcinoma) were included in this study. All of the participants underwent [(68) Ga]Ga-FAPI-04 and [F-18]-FDG imaging by positron emission tomography (PET)/computed tomography (CT) or PET/magnetic resonance (MR). The scans were interpreted by two experienced nuclear medicine physicians, and the maximum standardized uptake value (SUVmax) was calculated. Histopathological findings obtained from biopsy or resected surgical specimens were used as a reference for the final diagnosis. Results For the detection of primary gastric cancer, the sensitivities of [(68) Ga]Ga-FAPI-04 PET and [F-18]-FDG PET were 100% (38/38) and 82% (31/38), respectively (P = 0.016). Four cases of adenocarcinoma and three cases of signet ring cell carcinoma were missed by [F-18]-FDG PET. The mean SUVmax of [(68) Ga]Ga-FAPI-04 in tumours greater than 4 cm (11.0 +/- 4.5) was higher than that in tumours less than 4 cm (4.5 +/- 3.2) (P = 0.0015). The mean SUVmax of [(68) Ga]Ga-FAPI-04 was higher in T2-4 tumours (9.7 +/- 4.4) than in T1 tumours (3.1 +/- 1.5) (P = 0.0002). For the detection of metastatic lesions, the sensitivities of [(68) Ga]Ga-FAPI-04 PET and [F-18]-FDG PET in 10 patients with regional lymph node metastasis and distant metastasis were 6/10 and 5/10, respectively. Conclusion In this selected cohort, [(68) Ga]Ga-FAPI-04 PET had a superior detection rate than [F-18]-FDG PET for primary gastric cancer. [(68) Ga]Ga-FAPI-04 PET could provide better performance with regard to gastric cancer diagnosis and staging. Prospective clinical trials are warranted.