Evaluation of ⁶⁸ Ga-FAPI PET/CT and ¹⁸ F-FDG PET/CT for the primary staging of non-small cell lung cancer (NSCLC).

3071 Background: Fibroblast activation protein inhibitor (FAPI) radiolabeled with Gallium-68 or Fluorine-18 have emerged as promising tracers for targeting cancer-associated fibroblasts (CAFs) within the tumor microenvironment. Previous studies in lung cancer demonstrated that FAPI PET/CT is more sensitive in detecting metastases in the brain, lymph nodes, pleura, and bone. This study aimed to evaluate the clinical utility of FAPI PET/CT compared to FDG PET/CT for the primary staging of newly diagnosed NSCLC patients. Methods: This prospective study was done at Amrita Institute of Medical Sciences, Kochi between August 2022 to December 2023 among patients with newly diagnosed NSCLC who consented to undergo both scanning i.e. FDG as well as FAPI PET CT before initiating any treatment. This study was approved by institutional review board. Kolmogorov Smirnov one sample test was used to check the normality of data. To test the statistical significance of the difference in the average values of tumor volume, standardized uptake value (SUV), target to background ratio (TBR) and background uptake between FAPI and FDG, paired sample t test was used for normality and Wilcoxon signed rank test was used for non-normality. Results: In this study, 42 patients with newly diagnosed NSCLC (32 with adenocarcinoma (AC) and 10 with squamous cell carcinoma (SCC)) were included. Comparison of the results between FAPI and FDG PET in parameters like TBR, SUVmax and background value in metastatic lesions, FAPI performed better. In case of lymph nodes FAPI vs FDG, mean TBR was (5.06 ± 4.19 v/s 3.02 ± 2.89) p value=0.002 and in SUVmax value was (9.07 ± 5.1 v/s 6.59 ± 4.2) p value=0.01. Similar benefits were seen in TBR and SUVmax with FAPI on metastatic site like pleura and bone. In the primary lung lesion, mean tumour volume (MTV) was larger with FAPI but there was no difference in SUVmax, TBR and back ground uptake value. If we compare AC vs SCC cases, there was no advantage for SCC with FAPI in metastatic lesions as well as primary lesions. Driver mutated AC cases performed extremely well with FAPI. In brain, mean SUV max with FAPI was 4.52 ± 0.89 compared to 8.45 ± 3.31 with FDG. But the brain lesions identified with FAPI were higher than FDG due to higher TBR. In liver, SUV max was similar between FAPI and FDG but higher TBR was seen with FAPI. Conclusions: 68 Ga-FAPI PET/CT performed better than 18 F-FDG PET/CT in the primary staging of NSCLC. FAPI PET may be considered instead of FDG PET in staging of NSCLC. Patient compliance was also better because fasting and glycemic control was not required prior to FAPI. This is the only study where histology (AC and SCC) has been directly compared with both FAPI/PET vs FDG/PET – it shows FAPI/PET performs better with AC, and this South East Asian study showed FAPI/PET performs better with driver mutated NSCLC.