A Clinical Study to Evaluate the Pharmacokinetics, Efficacy, and Safety of Belumosudil in Chinese Adolescents With cGVHD Who Have Had an Inadequate Response to Glucocorticoids or Other Systemic Therapies

Prior treatment

• Received investigational systemic therapy for cGVHD within 28 days prior to enrollment, unless the prior treatment had been washed out for at least 28 days or 5 half-lives prior to enrollment, whichever is shorter.

Other illness

• Recurrence of hematologic neoplasms (according to the corresponding criteria for recurrence of primary hematologic neoplasms) or post-transplant lymphoproliferative disease at screening.
• Participant not suitable for participation, whatever the reason, as judged by the Investigator, including medical or clinical conditions, or participants potentially at risk of noncompliance to study procedures.

Lab values

• Absolute neutrophil count (ANC) \<1.0 × 10\^9/L.
• Platelet count \<50 × 10\^9/L.
• Alanine aminotransferase (ALT) \>3× the upper limit of normal (ULN), aspartate aminotransferase (AST) \>3 × ULN.
• Total bilirubin (TBIL) \>1.5 × ULN (\>3 ULN if Gilbert's syndrome).
• Estimated Glomerular Filtration Rate (eGFR) \<30 mL/min/1.73 m\^2 using the revised Bedside Schwartz formula . Revised Schwartz equation: CrCl (mL/min/1.73 m\^2) = 0.413 × (height \[in cm\])/Creatinine (in mg/dL) at screening visit.

Other

• Participants are excluded from the study if any of the following criteria apply:

• Participant must be 12 to less than 18 years of age at the time of signing the informed consent.
• Participant has undergone allogeneic hematopoietic stem cell transplantation (allo-HSCT).
• Has active moderate to severe cGVHD.
• Has received at least one line of prior systemic therapy for cGVHD.
• Participant must receive a corticosteroid therapy for cGVHD with a stable dose for at least 2 weeks prior to the first dose of the IMP.
• Has a Lansky-Play performance score of ≥60.
• Participants should have an expected survival of longer than 6 months.
• Body weight of 30 kg and above.
• Contraceptive use by men and women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
• The participant or their legally authorized representative (LAR) must be capable of giving signed informed consent.