A Study of Zasocitinib in Adults With Non-pustular Palmoplantar Psoriasis

Palmoplantar psoriasis (PPPsO) is a type of psoriasis that affects the palms of hands and soles of the feet. It can cause red, thick, scaly patches, and it is often associated with pain and itching. These symptoms can make daily life hard and can have a bigger effect on quality of life than psoriasis in some other areas of the body. Treatment can also be difficult because the skin on the palms and soles is thick, so treatments put on the skin (topical treatments) may not work as well. The main aim of this study is to find out how well zasocitinib works in reducing the skin redness, thickening, scaling, as well as fissures (narrow, elongated tears) on palms and soles of adults. Other aims are to learn if zasocitinib reduces the surface area of psoriasis on the palms and soles in adults with mainly Palmoplantar psoriasis. The study is conducted in 2 parts with a possibility of continued treatment (long-term extension). In Part 1, participants will receive zasocitinib for 4 months (16 weeks). Participants who finish Part 1 may be able to continue to Part 2 if the study doctor thinks they would benefit. Participants who continue to Part 2, will keep taking zasocitinib until they have been treated for about 1 year (52 weeks). After that, participants may choose to keep taking zasocitinib for another year (52 weeks). Participants will be followed for about 1 month (4 weeks) after the end of treatment. During the study, participants will visit their study clinic 16 times.