The first-in-class oral BTK inhibitor, ibrutinib (PCI-32765), has demonstrated impressive clinical responses in clinical trials as a single agent and has been subsequently approved by the FDA for the treatment of refractory MCL (November 2013), CLL (February 2014) and Waldenström’s macroglobulinemia (WM; January 2015) [115]. This evidence concerns the gene BTK and B-cell chronic lymphocytic leukemia.