Percentages of cell populations positive for leukemia by FISH 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. All 3 cell populations were highly leukemic at diagnosis. The CD34⁺CD38⁻ALDH^int population was highly enriched for leukemic cells (≥ 85%) in all disease phases, including complete cytogenetic remission (P > .5). In contrast, the total CD34⁺ population contained only a minority of leukemic cells (average, 22%; P < .001 vs diagnosis) in complete cytogenetic remission (patients 1, 15, and 16) but rose to more than or equal to 95% leukemic with progression to cytogenetic (patients 5, 7, and 12), or overt (patients 1 and 7-9) relapse (P = .001 for differences in total CD34⁺ and in mononuclear cell FISH percentages across all 4 disease phases).