Superior control of leukemic burden in PD166326-treated CML mice. (A) Spleen weight and (B) peripheral blood white blood cell (WBC) count of PD166326 (PD16; •)–, imatinib mesylate (▴)–, or placebo (▪)–treated CML mice at necropsy are shown by scatter plot. The median for each treatment group is depicted by the horizontal line. The P values for the differences in median spleen weight are PD166326 versus placebo (P < .001), PD166326 versus imatinib mesylate (P < .05), and imatinib mesylate versus placebo (P < .05). In the WBC count analysis only the PD166326 versus placebo comparison reached statistical significance (P < .01).