Assessment of flares in lupus patients enrolled in a phase II/III study of rituximab (EXPLORER)

The EXPLORER study was designed to assess the response to rituximab versus placebo in patients with moderate to severe extrarenal systemic lupus erythematosus (SLE) receiving background immunosuppression. The definition of response required reduced clinical activity without subsequent flares over 52 weeks, and the study did not meet its efficacy endpoint. The current exploratory analysis assessed flare rates in patients who achieved initial low disease activity response (British Isles Lupus Assessment Group [BILAG] C or better in all organs) during the study. Exploratory reanalysis of data from the EXPLORER trial was conducted, considering alternative definitions for flare. No difference was found between rituximab and placebo in preventing or delaying moderate to severe flares. However, when severe (BILAG A) flares alone were examined, rituximab reduced the risk of a subsequent first A flare (hazard ratio = 0.61; p = 0.052) and lowered mean ± SD annualized A flare rates (0.86 ± 1.47 vs. 1.41 ± 2.14; p = 0.038). Eighty-four (49.7%) rituximab-treated patients achieved low disease activity without subsequent A flares versus 31 (35.2%) placebo-treated patients ( p = 0.027). Prednisone rescue for A flares was similar in rituximab- (24%) and placebo-treated (14%) patients ( p = 0.204). This post hoc analysis evaluates the hypothesis that assessment of BILAG A flares may distinguish potential treatment effects with greater sensitivity than assessment of BILAG B flares.