Effect of imatinib on the expansion of c-kit–positive or c-kit–negative blast populations in peripheral blood. Values are derived from CD117 (c-kit)–FACS analysis of PB blast populations performed at time points indicated. Shown is a representative patient (PN 18) achieving a MR (> 50% reduction in c-kit–positive blast levels lasting ≥ 28 days) on imatinib treatment. ♦ indicates c-kit–positive PB blasts; ▪, c-kit–negative PB blasts.