Early BCR-ABL1 decline in imatinib-treated patients with chronic myeloid leukemia: results from a multicenter study of the Chinese CML alliance

An early molecular response is spectacularly predictive of outcome in chronic myeloid leukemia (CML) and early response landmarks may identify the high-risk patients likely to be benefit from an early therapy switch. In this study, we evaluated the most relevant cutoffs for early molecular response markers (BCR-ABL1 values at 3 months, log reduction and halving time between diagnosis and 3 months) in 476 first-line imatinib-treated Chinese patients with chronic phase CML. All outcomes were significantly superior for the 324 patients with 3-month BCR-ABL1 ≤10%, so did for the 270 patients with BCR-ABL1 >0.61 log reduction. BCR-ABL1 halving time ≤22 days was identified for patients with the most favorable outcome. Moreover, the prognosis was significantly poorest for patients with both halving time >44 days and BCR-ABL1 >10%. Importantly, multivariate regression analysis demonstrated that a BCR-ABL1 log reduction calculated at 3 months of 0.61 was the only variable that significantly predicted for OS. Our results highlight the importance of rapid initial decline of BCR-ABL1 in predicting satisfactory outcome. Our data support the evidence that monitoring BCR-ABL1 values at an early time point could contribute to accurately assess response and ultimately guide clinical decisions regarding the timing of therapeutic intervention.