Ibrutinib is the first-in-class oral covalent inhibitor of Bruton's tyrosine kinase that has been approved for the treatment of patients with chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL) and Waldenstrӧm’s macroglobulinemia (WM) due to its efficacy. The gene discussed is BTK; the disease is B-cell chronic lymphocytic leukemia.