BTK and B-cell chronic lymphocytic leukemia: The Bruton Tyrosin Kinase (BTK)-Inhibitor, Ibrutinib, is an established therapeutic agent for patients with B-cell malignancies such as relapsed or refractory chronic lymphocytic leukemia (CLL) (1, 2), mantle cell lymphoma (MCL) (3), and Waldenström macroglobulinemia (4).