Abstract
BACKGROUND: The identification of biomarkers predicting the treatment response of rheumatoid arthritis (RA) is important. [(68) Ga]Ga-FAPI-04 showed markedly increased uptake in the joints of patients with RA. The purpose of this study is to investigate whether [(68) Ga]Ga-FAPI-04 PET/CT can be a predictor of treatment response in RA. RESULTS: Nineteen patients diagnosed with RA in the prospective cohort study were finally enrolled. Both total synovitis uptake (TSU) and metabolic synovitis volume (MSV) in [(68) Ga]Ga-FAPI-04 and [(18)F]FDG PET/CT of the responders were significantly higher than those in non-responders according to Clinical Disease Activity Index (CDAI) and Simplified Disease Activity Index (SDAI) response criteria at 3-months' follow-up (P < 0.05). The PET joint count (PJC) detected in [(68) Ga]Ga-FAPI-04 and [(18)F]FDG PET/CT were also significantly higher in CDAI responders than non-responders (P = 0.016 and 0.045, respectively). The clinical characteristics of disease activity at baseline did not show significant difference between the responders and non-responders, except CRP (P = 0.035 and 0.033 in CDAI and SDAI response criteria, respectively). The baseline PJC(FAPI), TSU(FAPI) and MSV(FAPI) > cutoff values in [(68) Ga]Ga-FAPI-04 PET/CT successfully discriminated CDAI and SDAI responders and non-responders at 3-months' follow-up. CONCLUSION: [(68) Ga]Ga-FAPI-04 uptake at baseline were significantly higher in early responders than those in non-responders. Trial registration ClinicalTrials. NCT04514614. Registered 13 August 2020, https://register. CLINICALTRIALS: gov/prs/app/action/SelectProtocol?sid=S000A4PN&selectaction=Edit&uid=U0001JRW&ts=2&cx=-x9t7cp.