INTRODUCTION: In EVOLVE-MS-1 (NCT02634307), mean absolute lymphocyte count (ALC) on diroximel fumarate (DRF) declined from baseline by approximately 28% in year 1, then stabilized, similar to ALC decline observed with dimethyl fumarate (DMF). Prior studies reported that clinical efficacy of DMF was not substantially different in patients with and without lymphopenia.

METHODS: EVOLVE-MS-1-an open-label, 96-week, phase 3 study-assessed DRF safety and exploratory efficacy in patients with relapsing-remitting multiple sclerosis. This study analyzes efficacy-related outcomes comparing (1) patients with lymphopenia (≥ 1 ALC below lower limit of normal [LLN]) and without (all ALCs ≥ LLN); (2) across quartiles stratified by week 96 ALC decline from baseline: Q1 (≥ 47% decline); Q2 (30% to < 47% decline); Q3 (12% to < 30% decline); Q4 (< 12% decline).

RESULTS: Baseline characteristics were similar between patients without (n = 593) and with lymphopenia (n = 452). At week 96, adjusted annualized relapse rate (ARR; 95% confidence interval) was 0.14 (0.11-0.17) without lymphopenia and 0.12 (0.09-0.15) with lymphopenia. Estimated proportions with 12-week confirmed disability progression (CDP12) at week 96 were 10.2% without and 9.3% with lymphopenia. When stratified by quartiles (Q1-Q4), ARR at week 96 was 0.11 (Q1), 0.09 (Q2), 0.13 (Q3), and 0.17 (Q4). Estimated proportions with CDP12 at week 96 were 9.6% (Q1), 10.2% (Q2), 5.7% (Q3), and 10.9% (Q4). At week 96, no evidence of disease activity was achieved by 47.2% (Q1), 47.8% (Q2), 45.4% (Q3), and 37.3% (Q4) of patients.

CONCLUSION: In DRF-treated patients in EVOLVE-MS-1, clinical and radiological measurements indicated reduced disease activity regardless of lymphopenia or magnitude of ALC decline from baseline; however, patients who had greater ALC declines appeared to have numerically lower ARR and higher proportions free from relapses and gadolinium-enhancing lesions compared with those with smallest decline. This supports prior evidence that, while lymphopenia may contribute to fumarate efficacy outcomes, it is not the primary mechanism of action.

TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT02634307.