RETRACTED ARTICLE: Superiority of [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT to [ 18 F]FDG PET/CT in delineating the primary tumor and peritoneal metastasis in initial gastric cancer

Objective This study aimed to compare [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT with [ 18 F]FDG PET/CT in the evaluation of initial gastric cancer. Methods We retrospectively compared [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT with [ 18 F]FDG PET/CT in patients with initial gastric cancer from September 2020 to March 2021. Lesion detectability and the uptake of lesions quantified by the maximum standardized uptake value (SUVmax) and target-to-background ratio (TBR) were compared between the two modalities using the Wilcoxon signed-rank test, Mann–Whitney U test, and McNemar’s chi-square test. Results A total of 61 patients (37 males, aged 23–81 years) were included, of which 22 underwent radical gastrectomy. For primary lesions, higher uptake of [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 was observed compared to [ 18 F]FDG (median SUVmax, 14.60 vs 4.35, p < 0.001), resulting in higher positive detection using [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT than [ 18 F]FDG PET/CT (95.1% vs 73.8%, p < 0.001), particularly for tumors with signet-ring cell carcinoma (SRCC) (96.4% vs 57.1%, p < 0.001). [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT detected more positive lymph nodes than [ 18 F]FDG PET/CT (637 vs 407). However, both modalities underestimated N staging compared to pathological N staging. [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT showed a higher sensitivity (92.3% vs 53.8%, p = 0.002) and peritoneal cancer index score (18 vs 3, p < 0.001) in peritoneum metastasis and other suspect metastases compared to [ 18 F]FDG PET/CT. Conclusion Our findings indicate that [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT outperformed [ 18 F]FDG PET/CT in the evaluation of primary tumors with SRCC and peritoneum metastasis in initial gastric cancer. However, no clinically useful improvement was seen in N staging. Key Points • The uptake of [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 in primary tumor and metastasis was intensely higher than that of [ 18 F]FDG (p < 0.001) in 61 patients with initial gastric cancer . • [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT had a higher sensitivity detection in primary tumors (95.1% vs 73.8%, p < 0.001) and peritoneal metastases (92.3% vs 53.8%, p = 0.002) than [ 18 F]FDG PET/CT . • [ 68 Ga]Ga-FAPI-04/[ 18 F]FAPI-42 PET/CT depicted more positive lymph nodes than [ 18 F]FDG PET/CT (637 vs 407); however, both underestimated N staging compared to pathological N staging .