Association of High Serum Interleukin‐6 Levels With Severe Progression of Rheumatoid Arthritis and Increased Treatment Response Differentiating Sarilumab From Adalimumab or Methotrexate in a Post Hoc Analysis

Objective The development of biomarkers to guide treatment decisions is a major research focus in rheumatoid arthritis (RA). Patients with RA have elevated interleukin‐6 (IL‐6) levels; however, the utility of IL‐6 as a predictor of treatment response is unclear. This study was undertaken to investigate, by post hoc analysis, whether baseline IL‐6 levels are predictive of sarilumab treatment responses in 2 phase III studies. Methods Serum IL‐6 concentrations were measured in patients with RA prior to receiving sarilumab 200 mg (n = 148) or adalimumab 40 mg (n = 152) every 2 weeks (in the MONARCH trial; ClinicalTrials.gov identifier: NCT02332590) or sarilumab 150 mg, sarilumab 200 mg, or placebo every 2 weeks plus methotrexate (MTX) (n = 401, n = 396, and n = 397, respectively) (in the MOBILITY trial; ClinicalTrials.gov identifier: NCT01061736). Efficacy and patient‐reported outcomes were compared between and within groups according to IL‐6 tertile using linear and logistic regression. Results In MONARCH, patients with high baseline IL‐6 levels (all ≥3 times the upper limit of normal; n = 100) had higher disease activity at baseline than those with low IL‐6 levels (n = 100). The magnitude of clinical improvement over 24 weeks with sarilumab versus adalimumab was greater in patients with high compared to those with low baseline IL‐6 levels. In MOBILITY, compared to patients with low IL‐6 levels (n = 397), patients with high IL‐6 levels (n = 398) had higher disease activity and joint damage at baseline, were more likely to have joint progression, and had less clinical improvement over 52 weeks’ treatment with placebo plus MTX compared to sarilumab 150 mg or 200 mg plus MTX. Baseline IL‐6 and C‐reactive protein levels were both predictive of outcomes. Safety profiles were similar between defined IL‐6 tertiles. Conclusion IL‐6 may be a prognostic marker of disease progression and severity, and patients with high IL‐6 levels may be likely to benefit from sarilumab compared to adalimumab or MTX. Prospective validation is warranted to confirm the results of these post hoc analyses.