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Objectives LN increases the risk of end-stage kidney disease and mortality. Belimumab selectively inhibits B-lymphocyte stimulator, and has been shown to prevent organ damage progression in SLE and preserve kidney function in LN. We evaluated whether belimumab is associated with a lower risk of progression to LN among patients with SLE versus standard of care (SOC) in real-world practice.Methods A retrospective, longitudinal cohort study (GSK Study 217533) using claims linked with electronic health record data (Optum Market Clarity database). Index: date of initiation of belimumab or SOC (immunosuppressant [IS, except as LN initial therapy], intravenous glucocorticoids [GCs], or oral GC escalation to >=20 mg/day prednisone-equivalent) between 1 Jan 2017 and 31 Mar 2023. The unit of analysis was treatment episode. Patients could be included in both study cohorts. Adult patients had >=12 months’ continuous enrolment pre-index. Those with LN diagnosis or induction therapy before index date were excluded. Initiation of LN induction therapy was a proxy for incident LN, defined as earliest use of: subcutaneous belimumab 400 mg once weekly for four doses; voclosporin; cyclophosphamide; high-dose MMF. For each treatment episode, the observation period spanned index to earliest of: end of continuous enrolment or data availability; death; treatment switch. Time to initiation of LN induction therapy was assessed using a Cox proportional hazards (PH) model with a robust (Huber-White sandwich) variance estimator, weighted by average treatment effect among the treated weights (ATT-weights) based on propensity-score, and including covariates remaining imbalanced after weighting for a doubly robust approach.Results 1408 belimumab and 74,288 SOC patients contributed 3727 belimumab and 3621 SOC treatment episodes. Before weighting, belimumab patients were younger and more likely to have moderate than mild SLE severity and more treatment types at baseline. ATT-weighted baseline characteristics ( table 1) were similar between treatment cohorts. Use of IS, oral GC, and antimalarial therapies remained imbalanced after weighting and were further adjusted. Patients receiving belimumab had a significantly lower hazard of initiating LN induction therapy versus SOC (hazard ratio [95% CI]: 0.77 [0.62, 0.95]).Abstract PO:11:298 Table 1Select ATT-weighted baseline characteristicsConclusions These findings suggest potential renal protective effects through which belimumab may prevent progression to LN.Funding: GSKOriginal presentation: ACR 2025