BTK and B-cell chronic lymphocytic leukemia: Aberrant BTK signaling plays a critical role in the development of various B-cell malignancies including diffuse large B-cell lymphoma [21], CLL [22], mantle cell lymphoma (MCL) [23, 24], Waldenström macroglobulinemia (WM) [25, 26], and marginal zone lymphoma (MZL) [27].