[⁶⁸ Ga]Ga-FAPI-04 PET/CT may be a predictor for early treatment response in rheumatoid arthritis

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.

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 [¹⁸F]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 [¹⁸F]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.

[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.

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