F-FAPI-42 PET/CT for preoperatively identifying intrahepatic cholangiocarcinoma and hepatocellular carcinoma.

Background: Accurately differentiating hepatocellular carcinoma (HCC) from intrahepatic cholangiocarcinoma (ICC) is essential for therapeutic decision-making. This study aimed to explore the value of Fluor 18 (F)-conjugated fibroblast-activation protein inhibitor (FAPI-42) positron emission tomography-computed tomography (PET/CT) in distinguishing HCC from ICC preoperatively.

Methods: Patients with suspected intrahepatic lesions who underwent F-FAPI-42 PET/CT were retrospectively assessed and placed into an HCC group and an ICC group based on postoperative pathology. Clinical indicators and PET/CT metabolic parameters were documented. Univariate and multivariate logistic regression analyses identified the independent predictive factors. The receiver operating characteristic curve and the area under the receiver operating curve (AUC) were used to determine the diagnostic efficacy.

Results: A total of 48 patients (age 55.4±10.8 years; 35 males and 13 females), including 28 in the HCC and 20 in the ICC group, were included. Univariate analysis revealed significant differences in clinical indicators such as gender, platelet count, and hepatitis B surface antigen, carbohydrate antigen 19-9 (CA19-9), and alpha fetoprotein (AFP) levels between the groups (P<0.05). Metabolic parameters including the maximum standardized uptake value (SUVmax), the total lesion-FAPI (TL-FAPI), and the target-to-background ratio (TBR) were statistically different between groups (P<0.01), and patients with ICC had higher values than those with HCC, while the FAPI tumor volume (FAPI-TV) was not statistically different (P>0.05). Multivariate binary logistic regression analysis identified the SUVmax (P=0.003) as an independent predictor for ICC, and the AUC of the regression-based diagnostic model for predicting ICC was 0.914 at an optimal cutoff value of 12.13, with a sensitivity of 85.0% and a specificity of 89.3%.

Conclusions: SUVmax is an independent predictor for ICC. With the optimal cutoff value of 12.13, F-FAPI-42 PET/CT indicates good diagnostic efficacy in distinguishing between HCC and ICC.