BTK and B-cell chronic lymphocytic leukemia: Bruton’s tyrosine kinase (BTK) is a central kinase in the BCR axis that drives a signaling cascade leading to activation of NF-κB and phosphatidylinositol-3-kinase (PI3K) pro-survival pathways in CLL and the activated B-cell (ABC) subset of DLBCL [1, 3].