With the introduction of tyrosine kinase inhibitors that target the BCR-ABL fusion gene in chronic myeloid leukemia (CML), and with the introduction of agents targeting Bruton tyrosine kinase and their associated pathways in chronic lymphocytic leukemia (CLL), significant improvements have been made in survival of chronic leukemia. The gene discussed is BTK; the disease is B-cell chronic lymphocytic leukemia.