An Open-label Extension Trial of HZNP-HZN-825-301 in Adult Participants With Diffuse Cutaneous Systemic Sclerosis (Diffuse Cutaneous SSc)

Primary Objectives:The primary efficacy objective is to assess the efficacy of 52 weeks of open-label treatment with HZN-825 in participants with diffuse cutaneous systemic sclerosis, as measured by change from both baselines in forced vital capacity percent (FVC %) predicted.The primary safety objective is to examine the safety and tolerability of 52 weeks of open-label treatment with HZN-825, inclusive of, but not limited to, adverse events (AEs), serious AEs (SAEs) and the adverse event of special interest (AESI), from Day 1 to 4 weeks after last dose.

Key Inclusion Criteria:1. Completed the double-blind Treatment Period (Week 52) in Trial HZNP-HZN-825-301; participants prematurely discontinued from trial drug in Trial HZNP-HZN-825-301 for reasons other than safety or toxicity can be included at the discretion of the Investigator after completing Trial HZNP-HZN-825-301 scheduled visits, including Week 52 assessments.Key Exclusion Criteria:Anticipated use of another investigational agent for any condition during the course of the trial.Women of childbearing potential (WOCBP) or male participants not agreeing to use highly effective method(s) of birth control throughout the trial and for 4 weeks after last dose of trial drug as defined in the protocol.Any new development with the participant's disease or condition or any significant laboratory test abnormality during the course of Trial HZNP-HZN-825-301 that, in the opinion of the Investigator, would potentially put the subject at unacceptable risk.Pregnant or lactating women.Participants will be ineligible if, in the opinion of the Investigator, they are unlikely to comply with the trial protocol or have a concomitant disease or condition that could interfere with the conduct of the trial.