BackgroundEteplirsen received accelerated FDA approval for treatment of Duchenne muscular dystrophy (DMD) with mutations amenable to exon 51 skipping, based on demonstrated dystrophin production.ObjectiveTo report results from PROMOVI, a phase 3, multicenter, open-label study evaluating efficacy and safety of eteplirsen in a larger cohort.MethodsAmbulatory patients aged 7-16 years, with confirmed mutations amenable to exon 51 skipping, received eteplirsen 30 mg/kg/week intravenously for 96 weeks. An untreated cohort with DMD not amenable to exon 51 skipping was also enrolled.Results78/79 eteplirsen-treated patients completed 96 weeks of treatment. 15/30 untreated patients completed the study; this cohort was considered an inappropriate control group because of genotype-driven differences in clinical trajectory. At Week 96, eteplirsen-treated patients showed increased exon skipping (18.7-fold) and dystrophin protein (7-fold) versus baseline. Post-hoc comparisons with patients from eteplirsen phase 2 studies (4658-201/202) and mutation-matched external natural history controls confirmed previous results, suggesting clinically notable attenuation of decline on the 6-minute walk test over 96 weeks (PROMOVI: -68.9 m; phase 2 studies: -67.3 m; external controls: -133.8 m) and significant attenuation of percent predicted forced vital capacity annual decline (PROMOVI: -3.3%, phase 2 studies: -2.2%, external controls: -6.0%; p < 0.001). Adverse events were generally mild to moderate and unrelated to eteplirsen. Most frequent treatment-related adverse events were headache and vomiting; none led to treatment discontinuation.ConclusionsThis large, multicenter study contributes to the growing body of evidence for eteplirsen, confirming a positive treatment effect, favorable safety profile, and slowing of disease progression versus natural history.