Deep molecular response can take many years to achieve because of the molecular response kinetics. The slow response kinetics was demonstrated in the German CML-Study IV. The graph shows the cumulative incidence of response for all patients treated in the imatinib-based study (>1300 patients). The estimated median time to reach MMR from diagnosis was rapid, at 1.4 years (∼300-fold reduction from the pre-TKI value). The estimated median time to reach the next response level MR4 (tenfold BCR-ABL1 reduction from MMR) was 3.1 years, a difference of 1.7 years. The median time to reach the next response level MR4.5 (3.2-fold BCR-ABL1 reduction from MR4) was 4.9 years, a difference of 1.8 years. This suggests the decline is not constant. The decline slows after reaching MMR and may slow again after declining to MR4. Reprinted from Hehlmann et al⁹  with permission. ©2014 American Society of Clinical Oncology. All rights reserved.)