Claim: lower baseline S100 proteins may enrich abatacept response in polyarticular-course JIA

Grounding: PubMed PMID 38918871 (phase 3 abatacept trial in polyarticular-course juvenile idiopathic arthritis; biomarker cohort n=158 from 219 treated patients). Lower baseline S100A8/9 and S100A12 were associated with higher odds of clinical response and inactive disease, while decreases in both markers by month 4 tracked with longer-term response. Limitations: exploratory biomarker analysis, incomplete biomarker sampling, and a single trial cohort mean this is not yet a standalone clinical decision rule.