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

Purpose: This study aimed to explore the value of [Ga]Ga-labelled fibroblast activation protein inhibitor ([Ga]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[F]fluoro-D-glucose ([F]F-FDG) PET/CT.

Materials And Methods: Forty-seven treatment-naïve patients with newly diagnosed NPC underwent magnetic resonance imaging (MRI), [Ga]Ga-DOTA-FAPI-04 PET/CT and [F]F-FDG PET/CT within 1 week. 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, [Ga]Ga-FAPI PET/CT and [F]F-FDG PET/CT. Immunohistochemical (IHC) staining for FAP was conducted in 22 of the patients.

Results: [Ga]Ga-FAPI PET/CT outperformed [F]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, [Ga]Ga-FAPI PET/CT upgraded and underestimated T stage in 13 and 2 patients, while [F]F-FDG PET/CT upgraded and underestimated T stage in 5 and 13 patients. However, [Ga]Ga-FAPI PET/CT was inferior to [F]F-FDG PET/CT in diagnosing positive CLNs based on the analyses of patients, neck sides, neck levels and individual nodes. [Ga]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.

Conclusion: [Ga]Ga-FAPI PET/CT outperformed [F]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 [Ga]Ga-FAPI PET/CT is less promising for N staging because it detected fewer positive CLNs than [F]F-FDG PET/CT.