A Long-Term Study of Zasocitinib in Children and Teenagers With Plaque Psoriasis

The main aim of this study is to see how well the medicine zasocitinib works, how safe it is, and how children and teenagers aged 4 to under 18 with moderate-to-severe plaque psoriasis respond to it. The study will be done in 2 parts: Part A will include both children and teenagers, while part B will only include children. At first, only teenagers who meet the study rules can participate in this study. Children may only start to participate once enough information has been collected from other studies with zasocitinib. Participants in Part A will initially be assigned to receive either zasocitinib or placebo for the first 16 weeks of treatment, then all participants will receive zasocitinib through the end of the study. All participants in Part B will be assigned to receive treatment with zasocitinib throughout the study. Participants will be in the study for up to 4 years and 2 months (217 weeks), including up to 35 days for the screening period, 208 weeks of treatment (Part A and Part B) and a 4-week safety follow-up period. During the study, participants will visit their study site multiple times.