Glucocorticoid tapering and clinical outcomes during belimumab treatment in systemic lupus erythematosus: a retrospective real-world cohort study with exploratory renal analyses

To describe real-world clinical outcomes of belimumab (BEL) treatment in patients with systemic lupus erythematosus (SLE), with a particular focus on longitudinal glucocorticoid tapering and exploratory renal analyses. This single-center retrospective observational study included 46 patients with SLE who initiated BEL treatment between 2018 and 2025. Clinical and laboratory data, including prednisolone (PSL) dose, disease activity indices, serological markers, urine protein-to-creatinine ratio (UPCR), and estimated glomerular filtration rate (eGFR), were collected at baseline and during follow-up, when available. Longitudinal changes in concomitant background therapies were summarized descriptively. Exploratory renal analyses were performed in patients with lupus nephritis (LN) using changes in the UPCR and eGFR. Drug retention was evaluated using the Kaplan–Meier method. Renal histopathological analyses were performed in a subset with available biopsy data and were considered exploratory because of the heterogeneous clinical backgrounds and variable biopsy timing. The median PSL dose decreased from 10 mg/day at baseline to 8 mg/day at 24 weeks and 6 mg/day at 52 weeks after BEL initiation, with significant within-patient decreases at both time points (p < 0.001). Overall disease activity remained controlled, while complement levels improved during the follow-up. Among patients with LN (n = 12), UPCR showed a numerical decrease at 24 weeks (p = 0.055) and decreased at 52 weeks (p = 0.016) among patients with paired data, whereas the eGFR showed no significant change at either time point. Exploratory analyses did not identify significant associations between the available renal histopathological indices and changes in proteinuria. BEL treatment was continued in many patients during follow-up, although adverse events, including severe infections and death, were observed. In this real-world cohort, PSL doses decreased during follow-up after the initiation of BEL, while the overall disease activity remained controlled. In the small LN subgroup, the UPCR decreased at 52 weeks, and the eGFR remained stable. Because this study lacked a comparator group and the renal analyses were exploratory and limited by the small sample size, heterogeneous treatment backgrounds, and variable biopsy timing, these findings should be interpreted as within-patient observational data and require validation in future studies. What is already known about this subject? • Belimumab is effective in reducing disease activity in patients with systemic lupus erythematosus. • Its role in glucocorticoid tapering and renal outcomes in real-world clinical settings remains insufficiently characterized. What does this study add? • In this single-center real-world cohort, prednisolone doses decreased during follow-up after belimumab initiation, while overall disease activity remained controlled. • In the small lupus nephritis subgroup, the UPCR decreased at 52 weeks and the eGFR remained stable; however, these renal findings were exploratory and should not be interpreted as evidence of causal effects of treatment.