BTK and chronic graft versus host disease: Ibrutinib, a known Burton's tyrosine kinase (BTK) and interleukin-2 inducible T-cell kinase (ITK) inhibitor, is used for the treatment of B-cell disorders (chronic lymphocytic leukemia [CLL] and various other lymphomas) and chronic graft versus host disease following allogeneic hematopoietic cell transplantation.