BTK and B-cell chronic lymphocytic leukemia: Bruton tyrosine kinase inhibitors (BTKIs) are used for the treatment of several malignant hematological conditions, including chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) (1, –, 4), previously treated Waldenström macroglobulinemia (5, 6), relapsed/refractory follicular lymphoma (7), relapsed/refractory mantle cell lymphoma (8, –, 10), and relapsed/refractory marginal zone lymphoma (11).