293 Background: Signet ring cell carcinomas (SRC) is a well know limitation for FDG PET/CT. SRC is rich in cancer associated fibroblast hence can be imaged by FAPI PET/CT scan. This study aims to evaluate the diagnostic utility of 68Ga-FAPI PET/CT in the initial staging of signet-ring cell carcinoma (SRC) with a correlation with diagnostic laparoscopy for peritoneal metastasis. Methods: We included 29 histologically proven stomach SRC patients referred for staging work up. Both 68Ga-FAPI and 18F-FDG PET/CT scan were done with-in a week time. Diagnostic laparoscopy for peritoneal disease or any other site biopsy for metastatic site was used as a gold standard. Additionally, the single voxel maximum standard uptake value (SUVmax) of the primary, lymph node, metastasis, and SUVmean of the right lobe of the liver were recorded. SUVmax and target-to-background ratio (TBR) were compared with Wilcoxon's signed-rank test. While diagnostic effectiveness was compared with McNemar’s test. The study is ethically approved by institutional review board (RGCIRC/IRB-BHR/27/2025). Results: Out of 29 patients, FDG showed metastasis in 7 patients with diagnostic sensitivity, specificity, PPV, NPV and accuracy of 50.0%, 100%, 100%, 65%, and 74% and all these patients were also positive on FAPI scan. In remaining 22 non-metastatic patients on FDG scan, FAPI detected additional 6 patients with peritoneal metastasis. Diagnostic sensitivity, specificity, PPV, NPV and accuracy of FAPI was 85.7%, 100%, 100%, 86.6%, and 92.5% for metastasis. 13 patients were true negative on both FDG and FAPI PET for peritoneal metastasis. While 2 patients were falsely negative on both FDG and FAPI scans for peritoneal metastasis. One case was false negative in both FAPI and FDG for primary stomach lesion. 8/29 (27.5%) patients were upstaged by 68Ga-FAPI PET/CT scan in comparison to 18F-FDG PET/CT scan. Overall, FAPI PET/CT has impacted management in 24.1% of the patients in this cohort. Conclusions: 68Ga-FAPI PET/CT has higher diagnostic accuracy for metastatic workup in SRC stomach staging specially for peritoneal metastasis. Its superiority has been tailoring the diagnostic laparoscopy and guiding biopsy sites for better yield. Diagnostic statistics for metastasis for 18F-FDG and 68Ga-FAPI PET/CT scans. FDG FAPI Statistic Value 95% CI Value 95% CI Sensitivity 50.0% 23.1% to 76.9% 85.7% 57.1% to 98.2% Specificity 100.0% 75.2% to 100.0% 100.0% 75.2% to 100.0% Positive Predictive Value 100.0% 59.0% to 100.0% 100.0% 73.5% to 100.0% Negative Predictive Value 65.0% 52.3% to 75.8% 86.6% 64.3% to 95.9% Accuracy 74.0% 53.7% to 88.8% 92.5% 75.7% to 99.0%
Gupta et al. (Sat,) studied this question.