Optimal Time Points for BCR-ABL1 Tyrosine Kinase Domain Mutation Analysis on the Basis of European LeukemiaNet Recommendations in Chronic Myeloid Leukemia

BackgroundIn this study we aimed to evaluate appropriate time points for mutation analysis of chronic myeloid leukemia.Patients and MethodsIn total, 961 blood samples obtained from 605 chronic-phase chronic myeloid leukemia patients treated with imatinib were subjected to Sanger sequencing to detect BCR-ABL1 mutations. Mutation frequencies at landmark time points (3, 6, and 12 months) were assessed with 16 landmark responses defined by European LeukemiaNet and 2 additional responses, including a complete hematologic response (CHR) at 3 months and a complete cytogenetic response (CCyR) at 12 months.ResultsAfter 12 months of imatinib treatment of 605 patients, 28 (4.6%) patients harbored 33 mutations, including 23 (69.7%) highly resistant T315I and P-loop mutations. Sequencing data from 650 samples were compared with cytogenetic responses. The mutation frequencies in optimal, warning, and failure groups were 0.5% (2/430), 1.8% (2/110), and 19.1% (21/110), respectively. The molecular response was assessed using 956 samples, and the mutation frequencies were 0.7% (3/425), 3.4% (12/358), and 7.6% (14/173) for the optimal, warning, and failure groups, respectively. For the 2 additional responses, the mutation frequencies in patients with CHR at 3 months and with CCyR at 12 months were 0% (0/160) and 1.7% (4/242), respectively. Overall, mutations were frequently detected at 3-month cytogenetic failure (25.0%), 12-month cytogenetic failure (23.2%), and 6-month cytogenetic failure (10.5%) using response–mutation association analysis.ConclusionIrrespective of mutation frequency, failure of achievement of a cytogenetic response should be conducted with appropriate mutation analysis.