A Study of Belumosudil in Children With Chronic Graft Versus Host Disease (schoolROCK)

This is an open-label, single group, Phase 1/2, 1-arm study for treatment of children aged 1 to \<18 years with active moderate-to-severe cGVHD that is refractory to or recurred after at least 2 prior lines of systemic therapy for cGVHD. The purpose of Phase 1 is to determine the PK profiles and to establish the Recommended Pediatric Equivalent Dose (RPED) of belumosudil in participants aged 1 to \<12 years with active moderate to severe cGVHD. Upon completion and evaluation of Phase 1, Phase 2 will commence with the purpose of determining safety and efficacy (ORR by 24 weeks) of belumosudil in participants aged 1 to \<18 years. Study details include: The end of study is defined as 3 years after the last participant is recruited or all participants have discontinued treatment, or have died, whichever comes first. Minimum of 6 participants ages 1 to 6 years will be enrolled for each phase of study Individual participant duration on study will consist of: Up to 4 weeks for screening. Treatment until clinically significant progression of cGVHD, relapse/recurrence of the underlying disease, start of a new systemic treatment for cGVHD, experience of an unacceptable adverse event, request from participant or Investigator, or until the end of the study is reached, whichever comes first. 30 days of post treatment safety follow-up. Long-term follow-up until death or end of study, whichever occurs first.