Study of Efficacy and Safety of Ruxolitinib in Chinese Participants With Corticosteroid-refractory Chronic Graft vs. Host Disease

Inclusion Criteria: * Signed informed consent must be obtained prior to participation in the study. * Male or female Chinese participants aged 12 or older at the time of informed consent * Able to swallow tablets.- Have undergone alloSCT from any donor source (matched unrelated donor, sibling, haplo-identical) using bone marrow, peripheral blood stem cells, or cord blood. Recipients of non-myeloablative, myeloablative, and reduced intensity conditioning are eligible. * Evident myeloid and platelet engraftment: * Absolute neutrophil count (ANC) \>1,000/mm3 AND * Platelet count ≥25,000/mm3 Note: Use of growth factor supplementation and transfusion support is allowed during the trial, however, transfusion to reach a minimum platelet count for inclusion is not allowed during screening and at baseline. * Participants with clinically diagnosed cGvHD staging of moderate to severe according to NIH Consensus Criteria (Jagasia et al 2015) prior to Cycle 1 Day 1. * Moderate cGvHD: at least one organ (not lung) with a score of 2, 3 or more organs involved with a score of 1 in each organ, or lung score of 1. * Severe cGvHD: at least 1 organ with a score of 3, or lung score of 2 or 3. * Participants currently receiving systemic corticosteroids for the treatment of cGvHD for a duration of \< 12 months prior to Cycle 1 Day 1, and have a confirmed diagnosis of corticosteroid refractory cGvHD defined per 2014 NIH consensus criteria (Martin et al 2015) irrespective of the concomitant use of a calcineurin inhibitor, as follows: * A lack of response or disease progression after administration of minimum prednisone 1 mg/kg/day for at least 1 week (or equivalent) OR * Disease persistence without improvement despite continued treatment with prednisone at \>0.5 mg/kg/day or 1 mg/kg/every other day for at least 4 weeks (or equivalent) OR * Increase to prednisone dose to \>0.25 mg/kg/day after two unsuccessful attempts to taper the dose (or equivalent) * Participants has Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 Exclusion Criteria: For a full list of exclusion criteria, refer to Section 5.2. Key exclusion criteria include * Participants who have received two or more systemic treatments for cGvHD in addition to corticosteroids ± CNI for cGvHD. * Participants who have received ROCK2 inhibitors for cGvHD. * Participants that transition from active aGvHD to cGvHD without tapering off corticosteroids ± CNI and any systemic treatment Note: Participants receiving up to 30 mg by mouth once a day of hydrocortisone (i.e., physiologic replacement dose) of corticosteroids are allowed. * Participants who were treated with prior JAK inhibitors for aGvHD; except when the participant achieved complete or partial response and has been off JAK inhibitor treatment for at least 8 weeks prior to Cycle 1 Day 1. * Failed prior alloSCT within the past 6 months from Cycle 1 Day 1. * Participants with relapsed primary malignancy, or who have been treated for relapse after the alloSCT was performed. * SR-cGvHD occurring after a non-scheduled donor lymphocyte infusion (DLI) administered for pre-emptive treatment of malignancy recurrence. Participants who have received a scheduled DLI as part of their transplant procedure and not for management of malignancy relapse are eligible. Other protocol-defined inclusion/exclusion may apply.