Bruton’s tyrosine kinase (BTK) is a critical component of B-cell–receptor signaling that mediates interactions with the tumor microenvironment and promotes survival and proliferation of chronic lymphocytic leukemia (CLL) cells. Ibrutinib is a first-in-class oral covalent inhibitor of BTK designed for the treatment of B-cell cancers. In a phase 1b/2 study reported by Byrd and colleagues, ibrutinib treatment was found to produce high rates of durable responses in patients with relapsed or refractory CLL or small lymphocytic lymphoma.1
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