Mutational patterns revealed by cloning and sequencing of the BCR-ABL1 kinase domain region. Hypothetical mutation identities are designated A through H for discussion/explanation purposes. The range of mutation patterns revealed by cloning and sequencing when 2 BCR-ABL1 kinase domain mutations, A and B (green and red stars in the trace), are detected by direct sequencing are represented. This model encompasses all observed mutational patterns among the patients with 2 mutations evident by direct sequencing in this study. Detection of mutations A and B by direct sequencing can reflect their presence in the same BCR-ABL1 molecule (detected in 1 clone) or in different BCR-ABL1 molecules (detected in separate clones). The presence of both A and B in the same or different clones is signified as A/B or as A and B, respectively. In some compound mutant patients, clone A and clone B were observed separately in addition to clone A/B. Mutation A or B was sometimes coexistent with add-on mutations, for example, A/D and B/E. Predominant compound mutants could also acquire further add-on mutations as exemplified by A/B/C. Some mutations, such as F (single independent low-level mutants) or G/H (compound independent low-level mutants), were observed in clones that did not carry either predominant mutation, A or B.