Comparison of [68Ga]Ga-FAPI and [18F]FDG uptake in patients with gastric signet-ring-cell carcinoma: a multicenter retrospective study

Objective In this study, we investigated the role of [ 68 Ga]Ga-FAPI PET imaging in the detection of primary and metastatic gastric signet-ring-cell carcinoma (GSRCC) and compared with [ 18 F]FDG PET. Methods This retrospective multicenter analysis included 34 patients with histologically confirmed GSRCCs from four medical centers. The maximum standard uptake value (SUV max ), tumor-to-background ratio (TBR), and diagnostic accuracy were compared between the two modalities. [ 18 F]FDG and [ 68 Ga]Ga-FAPI uptakes were compared by using the Wilcoxon signed-rank test. McNemar’s test was used to compare the diagnostic accuracy between the two techniques. Results Data were analyzed from 27 paired PET/CT and 7 paired PET/MRI scans for 34 GSRCC patients (16 men and 18 women) who had a median age of 51 years (range: 25–85 years). [ 68 Ga]Ga-FAPI PET showed higher SUV max and TBR values than did [ 18 F]FDG PET in the primary tumors (SUV max : 5.2 vs. 2.2, p = 0.001; TBR: 7.6 vs. 1.3, p < 0.001), involved lymph nodes (SUV max : 6.8 vs. 2.5, p < 0.001; TBR: 5.8 vs. 1.3, p < 0.001), and bone and visceral metastases (SUV max : 6.5 vs. 2.4, p < 0.001; TBR: 6.3 vs. 1.3, p < 0.001). In diagnostic performance, [ 68 Ga]Ga-FAPI PET exhibited higher sensitivity than [ 18 F]FDG PET for detecting primary tumors (73% [16/22] vs. 18% [4/22], p < 0.001), local recurrences (100% [7/7] vs. 29% [2/7], p = 0.071), lymph node metastases (77% [59/77] vs. 23% [18/77], p < 0.001), and distant metastases (93% [207/222] vs. 39% [86/222], p < 0.001). Conclusion The results from this multicenter retrospective analysis justify the clinical use of [ 68 Ga]Ga-FAPI tracers for GSRCC diagnosis and staging. Key Points • [ 68 Ga]Ga-FAPI PET/CT is a promising imaging modality for the detection of primary and metastatic disease and has implications for TNM staging in GSRCC. • In this multicenter study of 34 patients with GSRCC, [ 68 Ga]Ga-FAPI PET exhibited greater radiotracer uptake, tumor-to-background ratios, and diagnostic accuracy than [ 18 F]FDG PET for detecting primary/recurrent tumors and metastatic lesions.