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

Objective In this study, we investigated the role of [Ga-68]Ga-FAPI PET imaging in the detection of primary and metastatic gastric signet-ring-cell carcinoma (GSRCC) and compared with [F-18]FDG PET. Methods This retrospective multicenter analysis included 34 patients with histologically confirmed GSRCCs from four medical centers. The maximum standard uptake value (SUVmax), tumor-to-background ratio (TBR), and diagnostic accuracy were compared between the two modalities. [F-18]FDG and [Ga-68]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). [Ga-68]Ga-FAPI PET showed higher SUVmax and TBR values than did [F-18]FDG PET in the primary tumors (SUVmax: 5.2 vs. 2.2, p = 0.001; TBR: 7.6 vs. 1.3, p < 0.001), involved lymph nodes (SUVmax: 6.8 vs. 2.5, p < 0.001; TBR: 5.8 vs. 1.3, p < 0.001), and bone and visceral metastases (SUVmax: 6.5 vs. 2.4, p < 0.001; TBR: 6.3 vs. 1.3, p < 0.001). In diagnostic performance, [Ga-68]Ga-FAPI PET exhibited higher sensitivity than [F-18]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 [Ga-68]Ga-FAPI tracers for GSRCC diagnosis and staging.