BTK and B-cell chronic lymphocytic leukemia: Bruton’s tyrosine kinase (BTK) is a key component of the B-cell receptor signaling pathway [3], and the first-generation BTK inhibitor, ibrutinib, has become a standard of care in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), mantle cell lymphoma, and Waldenström macroglobulinemia [5–13].