What is ibrutinib? What is its mechanism of action?

Ibrutinib (trade name Imbruvica), a small-molecule cancer drug, is designed to target an enzyme called Bruton's tyrosine kinase (BTK) and block (inhibit) its activity.

By binding to this tyrosine kinase enzyme's active region, ibrutinib interferes with the functions of B cells, which play an active role in immunity. Bruton's tyrosine kinase is associated with the B-cell receptor ; it participates in at least three critical parallel mechanisms: cell movement, attachment to a particular area (adhesion), and regulation of programmed cell death (apoptosis). By blocking these mechanisms in defense cells called B lymphocytes, ibrutinib is used both to treat blood and bone marrow cancers, certain leukemias and lymphomas, and when immune suppression is desired (for example, graft versus host disease).