This will be a combined retrospective and prospective cohort study, that will evaluate the incidence of de novo Systemic Lupus Erythematosus major organ manifestations (defined as BILAG A flares) in patients receiving belimumab (Arm A) and compare it to 2 standard-of-care groups (SoC) (Arm B: patients on SoC; Arm C: patients on SoC followed-up up to May 1st 2014, the first date where belimumab was available in Greece). The investigators will utilize survival analysis methods (Kaplan-Meier survival curves and Cox regression) and mixed effects longitudinal analyses. Additionally, the investigators will employ propensity score matching and/or inverse probability of treatment weighting, to create balanced cohorts and reduce bias.