Dasatinib therapy initiated at different times after leukemia initiation determines response to therapy. Weekly whole-animal luminescent imaging of recipients of 2 × 10⁵Arf^−/−p185⁺luc⁺ LICs were acquired over the course of a 4-week dasatinib treatment window (depicted by gray shading in each panel) and thereafter at indicated intervals until clinical relapse or termination of the experiment. Dasatinib therapy was begun in 3 cohorts of recipient mice that had acquired progressively increased leukemic burdens 3 (A), 7 (B), or 10 (C) days after receipt of LICs (Figure 1). Whole-animal luminescent signals (photons/s/cm²/sr) for each recipient mouse are plotted as solid lines that depict image intensity (ordinate) versus time in days after injection of LICs (abscissa). The empirically determined lower limit of sensitivity for whole-animal luminescence, derived from imaging of control nonleukemic animals, is indicated by the dotted line at the bottom of each panel. (D) Kaplan-Meier curves summarizing overall leukemia-free survival in each of the 3 cohorts of mice that received 4 weeks of continuous twice-daily (10 mg/kg/dose) dasatinib therapy.