BTK and B-cell chronic lymphocytic leukemia: Recent advances in treatment of patients with CLL have dramatically improved patient outcomes, prompted by innovations in drugs targeting B-cell receptor (BCR) signaling pathways including Bruton’s tyrosine kinase (BTK) [3–8] or phosphoinositide 3-kinases (PI3K) [9–13], or disruption of the B-cell lymphoma 2 (BCL2) [14–17] inhibitor of apoptosis, among others [18].