First-line imatinib can achieve efficacy similar to that with first-line nilotinib after standardized management in accordance with the European Leukemia Network recommendations. Treatment with imatinib as first-line treatment, with a switch to nilotinib after standardized management is feasible and effective. Both nilotinib and imatinib have been shown to be well tolerated and safe. Background: We investigated the real-life choice of first-line treatment in the chronic phase of chronic myeloid leukemia (CML-CP) and the feasibility of switching to nilotinib after first-line imatinib. Patients and Methods: We performed a retrospective analysis of the efficacy and safety of imatinib versus nilotinib as first-line therapy for patients with CML-CP. We also performed a comparative analysis of the efficacy of sustained imatinib versus a switch to nilotinib for patients with CML-CP with a warning or failure response or intolerance to imatinib. We also comparatively analyzed the efficacy between first-line nilotinib and first-line imatinib after standardized management in accordance with the European Leukemia Network (ELN) recommendations. A total of 344 patients were included in the present study. Results: The proportion of patients achieving a complete cytogenetic response (CCyR), major molecular response (MMR), and molecular response 4.0 (MR4.0) was greater with first-line nilotinib than with first-line imatinib at 0 to 24 and 0 to 36 months (P < .05). Of the 344 patients, 174 did not achieve an optimal response to first-line imatinib. A greater proportion of those patients who had switch to nilotinib had achieved a CCyR, MMR, and MR4.0 compared with those continuing imatinib for 12 months of subsequent treatment (P < .005). No difference was found in the proportion of patients with a CCyR, MMR, and MR4.0 between first-line nilotinib and first-line imatinib after standardized management in accordance with the ELN recommendations at 0 to 24 and 0 to 36 months (P > .05). Conclusion: First-line imatinib can result in efficacy similar to that with first-line nilotinib after standardized management in accordance with the ELN recommendations. Treatment with imatinib as first-line treatment, with a switch to nilotinib after standardized management is feasible and effective. (C) 2019 Elsevier Inc. All rights reserved.