A Study to Investigate the Comparative Effectiveness of Ibrutinib in Steroid Dependent/Refractory cGVHD Participants

Inclusion Criteria: Part A and Part B * Must have a confirmed diagnosis of steroid dependent or refractory classic cGVHD defined at any time post-hematopoietic cell transplantation (HCT) as: a) refractory disease - progressive cGVHD manifestations requiring prednisolone at greater than or equal to (\>=) 1 milligram per kilogram per day (mg/kg/day) for at least 1 week or persist without improvement despite continued treatment with glucocorticoid (prednisolone at \>= 0.5 mg/kg/day or 1 mg/kg every other day) for at least 4 weeks; b) dependent disease: persistent cGVHD manifestations requiring glucocorticoid \>= prednisolone 0.25 mg/kg/day or \>=0.5mg/kg every other day for at least 8 weeks Part A * Treated at least 2 or more therapies for cGVHD (including glucocorticoids) * Participants whose identified last line of conventional salvage treatment is second-fourth line of therapy * Index date (initiation date of the identified last-line of conventional salvage therapy) at least 28 weeks before the study initiation date Part B * Treated at least 3 lines therapies for cGVHD (including glucocorticoids) * Participants who are treated with ibrutinib in their second-fourth line of therapy Exclusion Criteria: Part A and Part B * Known or suspected active acute GVHD * Received an investigational drug (including investigational vaccines) or used an invasive investigational medical device within 28 days Part A * Treated with an investigational agent for their identified last-line of conventional salvage therapy * Pregnant, breastfeeding during last-line of conventional salvage therapy Part B * Pregnant, breast-feeding, or of childbearing potential without a negative serum or urine pregnancy test within 7 days of enrollment. Male or female participants of childbearing potential unwilling to use effective contraceptive precautions throughout the trial