Achieving early molecular response in chronic myeloid leukemia in chronic phase to reduce the risk of progression: clinical relevance of the 3- and 6-month time points.

Patients with chronic myeloid leukemia in chronic phase who achieve early molecular response (EMR; generally defined as BCR-ABL ≤ 10% on the International Scale at 3 or 6 months) have improved outcomes. However, there is no consensus on whether EMR failure at 3 months requires a change in therapy, and the value of the 6-month time point remains under debate. Some patients who do not achieve EMR at 3 months achieve significant decreases in BCR-ABL levels by 6 months, whereas others have progressive disease. For patients who do not achieve EMR at either time point, the risk of disease progression is higher both between 3 and 6 months and over the longer term, underlining the therapeutic relevance of the 3- to 6-month time period. For patients with EMR failure at 3 months, although there is currently no consensus on whether to switch therapy or wait until the 6-month assessment, some patients may benefit from an early change in treatment. This review synthesizes key clinical data demonstrating improved outcomes associated with the achievement of EMR and discusses the relevance of the 3- and 6-month time points on survival and the risk of disease progression. Several potential clinical situations are also presented to explore when a change in therapy may be considered.