Mutations were identified in 60 (60%) of these patients (all with imatinib-resistant CML-AP). Among the 60 patients with mutations, 26 unique imatinib-resistant mutations were identified, of which G250E was the most common (n = 9) (Table 5).

Seventeen different mutations in the BCR-ABL kinase domain were found in these 27 patients. Details of the mutations are given in Table 1….Died in AP (14), acquired imatinib resistance...Two of the 50 patients without detectable mutations acquired imatinib resistance. Therefore, of the 64 patients in late-CP, 13 acquired imatinib resistance and 11 (85%) of the 13 had detectable mutations.

Overall, these data indicate that the ENU-based assay faithfully reproduces the spectrum of mutations seen in patients with clinical resistance to imatinib mesylate...Spectrum and frequency of BCR-ABL kinase domain mutations recovered in the presence of imatinib mesylate, nilotinib, and dasatinib...Although both dasatinib and nilotinib are much more potent than imatinib mesylate and have activity against most kinase domain mutants, it is conceivable that their specific modes of binding to Abl may lead to new “vulnerable” sites that could confer drug resistance.

CONTRADICTING EVIDENCE: In our study, we investigated the activity of bosutinib, dasatinib, imatinib, and nilotinib against a panel of 18 mutated forms of BCR/ABL associated with imatinib resistance in CML and Ph+ acute lymphoblastic leukemia patients. The results are listed in Figure 1 (Table 1 lists all the actual values for the relative concentration that inhibits 50%).