A comparative study of [68Ga]Ga-FAPI-04 PET/MR and [18F]FDG PET/CT in the diagnostic accuracy and resectability prediction of ovarian cancer

Abstract

Purpose: To provide a theory for guiding clinical treatment by comparing the clinical application value of [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) PET/CT and [⁶⁸Ga]Ga-FAPI (fibroblast activating protein inhibitor) PET/MR in the diagnosis and evaluation of resectability of ovarian cancer.

Methods: Thirty patients with high clinical suspicion of ovarian malignancies were enrolled from July 2021 to October 2022 and underwent [¹⁸F]FDG PET/CT and [⁶⁸Ga]Ga-FAPI-04 PET/MR within 5 days. Twenty patients underwent [¹⁸F]FDG PET/MR at once completing [¹⁸F]FDG PET/CT for consistency checking. Images were analysed for comparing SUVs and for judging incomplete resectability according to the peritoneal cancer index (PCI) and SUIDAN scoring system. The expression of FAP, HK2 and Ki67 was analysed by immunohistochemistry staining.

Results: There was no significant difference between PET/MR and PET/CT in SUVs_-FDG at different locations (p > 0.05), and their diagnostic accuracies were similar. The diagnostic accuracy of [⁶⁸Ga]Ga-FAPI-04 PET/MR had advantages for peritoneal metastasis since SUVs_FAPI were higher (p < 0.01). The sensitivity of [⁶⁸Ga]Ga-FAPI-04 PET/MR in the diagnosis of peridiaghragmatic metastases was higher because SUV_max in the liver was decreased (p < 0.001). [⁶⁸Ga]Ga-FAPI-04 PET/MR might have advantages in diagnosing gastrointestinal invasion. In PCI score analysis, [⁶⁸Ga]Ga-FAPI-04 PET/MR could partially correct missing or underestimated scores by [¹⁸F]FDG PET/CT, but the matching probability between left peri-intestinal metastasis scores was low and easy to overestimate. Interestingly, diaphragmatic metastasis detected by [⁶⁸Ga]Ga-FAPI-04 PET/MR had the greatest correlation with the prediction of incomplete resectability (logistic regression p = 0.02). Through immunohistochemistry, the expression of FAP had a strong correlation with SUV_max-FAPI (p < 0.001), while the expression of HK2 was correlated with SUV_max-FDG (p < 0.01). In addition, SUV_max-FDG with Ki67 ≥ 20% was significantly higher than that with Ki67 < 20% (p < 0.05).

Conclusions: [⁶⁸Ga]Ga-FAPI-04 PET/MR had obvious advantages for metastases diagnosis and could more accurately assess tumour load and predict incomplete resectability. SUV_max-FDG was conducive to evaluating the degree of tumour malignancy.

Keywords: Degree of malignancy; Ovarian cancer; PET/MR; Resectability; [18F]FDG; [68Ga]Ga-FAPI-04.