Phase 3 Trial of Pamrevlumab or Placebo in Combination With Systemic Corticosteroids in Participants With Ambulatory DMD

This is a global, randomized, double-blind, trial of pamrevlumab or placebo in combination with systemic corticosteroids in participants with DMD, aged 6 to \<12 years (ambulatory participants only). Approximately 70 participants will be randomized at a 1:1 ratio to Arm A (pamrevlumab + systemic deflazacort or equivalent potency of corticosteroids administered orally) or Arm B (placebo+ systemic deflazacort or equivalent potency of corticosteroids administered orally), respectively. Randomization will be stratified by exon 44 deletion for analysis. Stratification has no impact upon treatment assignment nor dosage. Participants must be fully informed of the potential benefits of approved products and make an informed decision when participating in a clinical trial in which they could be randomized to placebo. The main study has 3 study periods: * Screening period: Up to 4 weeks * Treatment period: 52 weeks * Safety Follow-up period/final assessment: A visit 28 days (+/- 3 Days) and a final safety follow-up phone call 60 days (+ 3 Days) after the last dose Each participant will receive pamrevlumab or placebo at 35 mg/kg every 2 weeks for up to 52 weeks. Participants who complete 52 weeks of treatment may be eligible for an open-label extension (OLE), offering extended treatment with pamrevlumab. Participants who discontinue study treatment for any reason should be encouraged to return to the investigative site to complete final safety and efficacy assessments.