BTK and B-cell chronic lymphocytic leukemia: Ibrutinib: Ibrutinib, an irreversible BTK inhibitor, was initially approved by the FDA in 2013 for the treatment of mantle cell lymphoma (MCL) and later in 2014 for chronic lymphocytic leukemia (CLL) and in 2015 for Waldenström’s macroglobulinemia [34].