The treatment of Philadelphia chromosome-positive (Ph+) leukemias has improved markedly. There are some inhibitors of Bcr-Abl tyrosine kinase (TK) that are effective for Ph<sup>+</sup> leukemias. However, resistance to imatinib can develop by various molecular mechanisms. They include Bcr-Abl overexpression, mutations within the imatinib-binding site of Bcr-Abl, expression of a...