Clinical prospective study of Gallium 68 (68Ga)–labeled fibroblast-activation protein inhibitor PET/CT in the diagnosis of biliary tract carcinoma

Abstract Purpose To investigate the 68 Ga–labeled fibroblast-activation protein inhibitor ( 68 Ga-FAPI) PET/CT diagnosis performance in biliary tract carcinoma (BTC), and analyze the association between 68 Ga-FAPI PET/CT and clinical indexes. Methods A prospective study (NCT 05264688) was performed between January 2022 through July 2022. Fifty participants were scanned using 68 Ga-FAPI and 18 F-FDG PET/CT and acquired pathological tissue. We employed the Wilcoxon signed-rank test to compare the uptake of 68 Ga-FAPI and 18 F-FDG, and the McNemar test was used to compare the diagnostic efficacy between the two tracers. Spearman or Pearson correlation was used to assess the association between 68 Ga-FAPI PET/CT and clinical indexes. Results In total, 47 participants (mean age 59.09±10.98 [range 33–80 years]) were evaluated. The 68 Ga-FAPI detection rate was greater than 18 F-FDG in primary tumors (97.62% vs. 85.71%), nodal metastases (90.05% vs. 87.06%), distant metastases (100% vs. 83.67%). The uptake of 68 Ga-FAPI was higher than 18 F-FDG in primary lesions (intrahepatic cholangiocarcinoma: 18.95±7.47 vs. 11.86±0.70, p=0.001; extrahepatic cholangiocarcinoma:14.57±6.16 vs. 8.80±4.74, p=0.004), abdomen and pelvic cavity nodal metastases (6.91±6.56 vs. 3.94±2.83, p<0.001), distant metastases (pleural, peritoneum, omentum, and mesentery: 6.37±4.21 vs. 4.50±1.96, p=0.01; Bone: 12.15±6.43 vs. 7.51±4.54, p=0.008). There was a significant correlation between 68 Ga-FAPI uptake and FAP expression (Spearman r=0.432, p=0.009), carcinoembryonic antigen (CEA) (Pearson r=0.364, p=0.012), and platelet (PLT) (Pearson r=0.35, p=0.016). Meanwhile, a significant relationship between 68 Ga-FAPI metabolic tumor volume (MTV) and carbohydrate antigen199 (CA199) (Pearson r=0.436, p=0.002) was confirmed. Conclusion 68 Ga-FAPI preceded 18 F-FDG in diagnosing BTC to a certain extent. The correlation between 68 Ga-FAPI PET/CT indexes and FAP expression, CEA, PLT, and CA199 were confirmed.