BCR-ABL expression in individual BCR-ABL-positive hematopoietic colonies. The determination of BCR-ABL/ABL ratios was performed according to the international scale (IS) standardization by quantitative RT-PCR on individual hematopoietic colonies from CFU-C (colony forming unit-cell) and LTC-IC (long-term culture-initiating cell) assays. Dots represent BCR-ABL/ABL ratios for single colonies (CFU-Cs or LTC-ICs) from a patient resistant to tyrosine kinase inhibitor therapy and from 6 patients with undetectable molecular residual disease (UMRD) for more than 3 years. Mann Whitney U tests were used to estimate differences between groups. Significant differences are reported after Bonferroni correction to account for multiple testing. The horizontal lines indicate median BCR-ABL/ABL ratios, and the number of BCR-ABL–positive CFU-Cs and LTC-ICs analyzed in the study is shown.