The initial efficacy of ibrutinib was confirmed by Ki67 staining of TCL1-CLL cells showing a dramatic reduction of cell proliferation in blood, spleen, bone marrow and lymph nodes after 1 week of ibrutinib treatment (I-early) in comparison to the vehicle group (V-early) (Fig. 1C). The gene discussed is MKI67; the disease is B-cell chronic lymphocytic leukemia.