This is a single group, Phase 4, single-arm post-marketing study for treatment.

The purpose of this study is to verify the pharmacokinetics, efficacy, and safety of belumosudil mesylate tablets in Chinese adolescent participants (aged from 12 to less than 18) with cGVHD who have had an inadequate response to glucocorticoids or other systemic therapies.

Participants will receive treatment with belumosudil tablets 200 mg once daily in 28-day cycles during the study.

Inclusion Criteria:

• 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.

Exclusion Criteria:

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

• Recurrence of hematologic neoplasms (according to the corresponding criteria for recurrence of primary hematologic neoplasms) or post-transplant lymphoproliferative disease at screening.
• 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.
• 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.
• 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.

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org