68Ga]Ga-FAPI PET/CT Improves the T Staging of Patients with Newly Diagnosed Nasopharyngeal Carcinoma: A Comparison with [18F]F-FDG.

Abstract

This study aimed to explore the value of [68Ga]Ga-labelled fibroblast activation protein inhibitor ([68Ga]Ga-FAPI) positron emission tomography/computed tomography (PET/CT) in the initial staging of patients with newly diagnosed nasopharyngeal carcinoma (NPC), compared with 2-deoxy-2[18F]fluoro-D-glucose([18F]F-FDG) PET/CT. Forty-seven treatment-naïve patients with newly diagnosed NPC underwent magnetic resonance imaging (MRI), [68Ga]Ga-DOTA-FAPI-04 PET/CT and [18F]F-FDG PET/CT within 1week. The diagnostic efficiency of all imaging modalities for evaluating primary tumour extension was compared from the two aspects of soft tissue and bony structure involvement. The accuracy of two PET/CT methods for diagnosing cervical lymph node (CLN) metastases was compared, and MRI served as the standard reference. T and N stages were assessed by MRI, [68Ga]Ga-FAPI PET/CT and [18F]F-FDG PET/CT. Immunohistochemical (IHC) staining for FAP was conducted in 22 of the patients. [68Ga]Ga-FAPI PET/CT outperformed [18F]F-FDG PET/CT in the assessment of primary tumour invasion in the cavernous sinus (10 vs. 1, p < 0.001) and bony structures (207 vs. 177, p < 0.001). Compared with MRI, [68Ga]Ga-FAPI PET/CT upgraded and underestimated T stage in 13 and 2 patients, while [18F]F-FDG PET/CT upgraded and underestimated T stage in 5 and 13 patients. However, [68Ga]Ga-FAPI PET/CT was inferior to [18F]F-FDG PET/CT in diagnosing positive CLNs based on the analyses of patients, neck sides, neck levels and individual nodes. [68Ga]Ga-FAPI PET/CT changed therapeutic schedules in 8 patients because of stage group changes. The presence of FAP with high quantity and intensity in cancer-associated fibroblasts (CAFs) was confirmed in all tumour specimens. [68Ga]Ga-FAPI PET/CT outperformed [18F]F-FDG PET/CT in detecting the cavernous sinus and bony structure involvement of primary NPC tumours, suggesting its value in improving T staging and therapeutic regimen selection. However, the performance of [68Ga]Ga-FAPI PET/CT is less promising for N staging because it detected fewer positive CLNs than [18F]F-FDG PET/CT.