Ibrutinib inhibits tumor proliferation in lymph node and bone marrow. (A) A representative histogram of Ki67 staining on CLL cells in the lymph node (LN). Isotype control is represented by the gray shaded area, the dashed line represents pretreatment, and the solid black line day 2. (B) Mononuclear cells from LN (n = 8) or bone marrow (BM) aspirates (n = 10) were fixed, permeabilized, and stained with the indicated antibody. Results shown are for the CLL population (CD5⁺/CD19⁺). The mean (± SEM) percent of Ki67 expressing CLL cells pretreatment and on ibrutinib is shown. Comparisons are by paired Student t test. (C) Images of LN tissue obtained pretreatment and on day 2 of ibrutinib stained with hematoxylin and eosin (H&E) and anti Ki67 were captured at ×40 magnification on an Olympus Bx41 microscope. (D) The percent of CLL cells expressing Ki67 at various clinical time points in the PB is shown (n = 20). Significance compared with pretreatment was determined by a paired Student t test and is indicated by asterisks: ***P < .001.