DOES ADDING CONCOMITANT IMMUNOSUPPRESSIVE THERAPY TO BELIMUMAB PROVIDE ADDITIONAL BENEFITS IN SLE? ANALYSIS FROM BEL-SPAIN: THE SPANISH BELIMUMAB MULTICENTER REGISTRY

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PV257 / #666 Poster Topic: AS24 - SLE-Treatment Background/Purpose Although belimumab has shown efficacy and safety as an adjunct to standard therapies such as immunosuppressive agents in treating systemic lupus erythematosus (SLE), its role as monotherapy is less well defined. Using data from a national belimumab registry, this study aims to assess whether the addition of immunosuppressive therapy (IS) to belimumab yields additional clinical benefits compared to belimumab monotherapy. Methods This retrospective longitudinal study analyzed data from the Spanish Belimumab Registry (BEL-Spain). Patients were included if they had completed at least 12 months of belimumab treatment and had documented data on the use of concomitant IS at the 12-month follow-up. Patients were grouped based on IS use at 12 months, and data from baseline, 6-month, and 12-month visits were analyzed. Outcomes assessed included the Lupus Low Disease Activity State (LLDAS), DORIS-21 remission criteria, physician-assessed response, flare rates (SFI), and glucocorticoid (GC) usage. To address potential confounding, given that patients receiving combined therapy (belimumab+IS) are more likely to have more severe disease, overlap propensity score (PS) weighting was performed. The PS for receiving combined treatment was estimated using a multivariable logistic regression model, which included covariates such as age, disease duration, baseline disease activity (SLEDAI), GC dose, and the number of flares prior to starting belimumab. The primary outcome was the rate of DORIS-21 remission after 12 months of belimumab treatment Results Of the 377 patients in the registry as of November 2024, 258 met the inclusion criteria. Among these, 236 (91.5%) were female, and 218 (85.5%) were Caucasian. The mean age at belimumab initiation was 41.9 years (SD 12.6), with a mean disease duration of 11.4 years (SD 11). The baseline SLEDAI score was 11.8 (SD 10.5), and the mean SLICC Damage Index was 0.76 (SD 1.17). Of the 258 patients, 177 were receiving concomitant IS at 12 months, while 81 were not. Table 1 compares the 2 groups in terms of disease activity indices and treatment response. At 6 and 12 months, there were no statistically significant differences between groups in the number of flares (including severe flares), physician-assessed response, or response in terms of achieving a DORIS-21 or LLDAS status. Although the concomitant IS group had a higher baseline SLEDAI, the change over time was similar between groups. Regarding GC use, more patients in the IS group were receiving GCs; however, the average dose was comparable between groups. Figure 1 illustrates patient treatment trajectories based on the use of concomitant IS over 12 months. After applying overlap propensity score weighting, baseline covariates between the 2 groups were perfectly balanced. The percentage of patients achieving DORIS-21 remission after weighting was 25% vs 33% at 6 months, and 43% vs 46% at 12 months, in the IS and non-IS groups, respectively. Logistic regression analyses with overlap weighting yielded odds ratios (ORs) of 0.68 (95% CI 0.26–1.77, p 0.43) for DORIS-21 remission at 6 months, and 0.89 (95% CI 0.37–2.14, p 0.77) at 12 months. Table 1: Baseline Characteristics and Treatment Response in Patients Receiving Belimumab With or Without Concomitant Immunosuppressive Therapy at 12 Months. Figure 1: Patient treatment trajectories based on the use of concomitant IS over 12 months Conclusions According to BEL-Spain Registry data, the addition of concomitant IS to belimumab did not appears to confer major additional clinical benefits in terms of disease activity reduction, flare rate, or treatment response. These findings suggest that belimumab monotherapy may be a viable option for certain SLE patients. Prospective studies are needed to validate these observations and to identify patient subgroups who may benefit from combination therapy.