This trial was to evaluate the CCyR rate at 12 months of nilotinib therapy when compared to imatinib treatment in patients with suboptimal response to imatinib. The patients were stratified by prior duration of initial imatinib treatment, and were randomized to receive either 400 mg/twice daily of continuous nilotinib or imatinib treatment. The first stratum patients were treated with imatinib = 6 to < 12 months and having at least a minimal cytogenetic, but no partial cytogenetic response; and the second stratum patients were treated with imatinib = 12 months to < 18 months and having partial cytogenetic response (PCyR), but no CCyR.