Predicted change in 3-month response category according to the day of sample collection. A BCR-ABL1 value of 10% at 3 months discriminates between treatment failure or a warning and an optimal response according to current recommendations and guidelines. (A-D) Plots of the actual BCR-ABL1 decline for 4 patients with multiple BCR-ABL1 measurements within the first 3 months of imatinib treatment. The circles are the actual BCR-ABL1 values of the sample collections at baseline and the 1-, 2-, and 3-month time points. The decline was exponential in each patient as indicated by the correlation coefficient of the regression line r. The actual day of the 3-month collection from the imatinib start date and the actual BCR-ABL1 values are indicated within each graph in bold. The shaded region represents the 56-day measurement window over which the 3-month samples in our cohort were collected (days 70-126). The dashed lines represent the continuation of the regression line within the measurement window. The halving times at 1, 2, and 3 months were each calculated using the individual patient’s baseline value. We estimated the BCR-ABL1 values for the extremes of the measurement window (day 70 and day 126) for each patient, using the known 3-month halving time, the patient’s baseline BCR-ABL1 value, and by varying the day of sample collection in the formula. This assumes the decline remains constant within the measurement window. The actual and estimated BCR-ABL1 values for each patient on the actual day of the 3-month sample collection were almost identical in each case, which are indicated in bold text. The asterisk indicates the collection day where the response classification would change.