Composition of the total leukemic burden by cell populations in each disease phase. Data are shown only for those patient samples with a FISH-detectable cytogenetic abnormality and a detectable CD34⁺ CD38⁻ALDH^int population. The total leukemic burden is assumed to be 10¹² cells at diagnosis.³⁷  Each vertical bar represents the total leukemic (mononuclear) cell burden (based on FISH) for each disease phase: initial diagnosis (patients 1-3, 5, 6, 8-13, and 22), cytogenetic CR with the “MRD” pattern (patients 1, 15, and 16), cytogenetic relapse (with FISH, but not morphologic, evidence of disease; patients 5, 7, and 12), and at overt relapse (patients 1 and 7-9). The CD34⁺ CD38⁻ALDH^int cells represented an average of 2% (range, 0.3%-7%) of the total leukemic burden at initial diagnosis, 34% (range, 9%-51%) in cytogenetic CR, 8% (range, 2%-12%) in cytogenetic relapse, and 1% (range, 0.5%-2%) at overt relapse (P < .001). The CD34⁺ CD38⁻ALDH^int population constituted an average of 8% (5%-13%) of the total leukemic CD34⁺ cells at initial diagnosis, 34% (range, 9%-51%) in cytogenetic CR (P < .001 vs initial diagnosis), 18% (range, 7%-37%) in cytogenetic relapse, and 7% (range, 2%-16%) in overt relapse. Although the total leukemic burden decreased by more than 2 logs from diagnosis to cytogenetic CR (P < .001), the absolute size CD34⁺ CD38⁻ALDH^int population decreased only by 1 log (P = .4).