Ibrutinib improves OS in mice transplanted with TCL1 leukemia. After transplantation with leukemic TCL1 spleen lymphocytes, SCID mice were followed for leukemia development, and once leukemic, randomized to treatment with ibrutinib or vehicle. Mice treated with ibrutinib (n = 8) survived significantly longer than those treated with vehicle (n = 9; P = .003).