Clinical Utility of F-18 Labeled Fibroblast Activation Protein Inhibitor (FAPI) for Primary Staging in Lung Adenocarcinoma: a Prospective Study

Purpose The purpose of this study was to compare the primary staging of F-18 labeled fibroblast activation protein inhibitor ([F-18]F-FAPI) with that of F-18 labeled fluordesoxyglucose positron emission tomography/computed tomography ([F-18]F-FDG PET/CT) in patients with lung adenocarcinoma (LAD). Procedures We prospectively analyzed the images of LAD patients who underwent [F-18]F-FAPI and [F-18]F-FDG PET/CT between May 2020 and August 2021. [F-18]F-FAPI and [F-18]F-FDG uptakes were compared using the paired samples t test, and lesion numbers were compared using the Wilcoxon signed-rank test. Results Thirty-four LAD patients were evaluated. Patients showed high [F-18]F-FAPI uptake in primary lesions (SUVmax 12.54 +/- 3.77). Both [F-18]F-FAPI and [F-18]F-FDG had 100% detection rates for primary tumors. However, [F-18]F-FAPI showed higher SUVmax than [F-18]F-FDG in lesions of the lymph nodes, pleura, bones, and other tissues (all P <= 0.05). Although the absolute uptake values of [F-18]F-FAPI in brain lesions were lower than those of [F-18]F-FDG (1.56 +/- 2.19 vs.7.34 +/- 3.54, P < 0.0001), the tumor-to-background (T/B) ratios were significantly higher than those of [F-18]F-FDG (9.53 +/- 12.07 vs.1.01 +/- 0.49, P < 0.0001). Generally, [F-18]F-FAPI PET/CT could visualize more total lesions than [F-18]F-FDG (554 vs.464, P = 0.003), especially in lymph nodes (258 vs.229, P = 0.039), the brain (34 vs.9, P = 0.002), and pleura (56 vs.30, P = 0.041). However, contrast-enhanced brain magnetic-resonance imaging (MRI) showed more brain lesions than [F-18]F-FAPI PET/CT (56 vs.34, P = 0.002). Compared with the [F-18]F-FDG-based TNM stage, the [F-18]F-FAPI-based TNM stage was upgraded in six patients (17.6%). Conclusions [F-18]F-FAPI PET/CT showed a very high detection rate for primary LAD. In addition, F-18-FAPI PET/CT demonstrated clearer tumor delineation and more lesions than [F-18]F-FDG PET/CT, especially in lymph nodes, the brain, and pleura. Therefore, [F-18]F-FAPI had an advantage over [F-18]F-FDG for primary staging of LAD. However, brain MRI could identify more and smaller lesions than [F-18]F-FAPI PET/CT.

Automated summary

The study compared the primary staging of F-18 labeled fibroblast activation protein inhibitor ([F-18]F-FAPI) with that of F-18 labeled fluordesoxyglucose positron emission tomography/computed tomography ([F-18]F-FDG PET/CT) in patients with lung adenocarcinoma (LAD). The results showed that [F-18]F-FAPI PET/CT had a high detection rate for primary LAD and provided clearer tumor delineation and more lesions, especially in lymph nodes, the brain, and pleura. However, brain MRI could identify more and smaller lesions than [F-18]F-FAPI PET/CT.