- Patients must have failed therapy with imatinib mesylate. Failure will be defined as: 1) patients who have failed to achieve or have lost a complete hematologic remission at 3 months from the start of therapy with imatinib mesylate, or 2) patients who have failed to achieve or have lost at least a minimal cytogenetic response after 6 months of therapy with imatinib mesylate, or 3) patients who have failed to achieve or have lost a major cytogenetic response after 12 months of therapy with imatinib mesylate