During treatment with a TKI (tyrosine kinase inhibitor), regular tests are needed to ensure that you’re responding to the medication. The amount of disease suppression is reported according to the reduction in leukemia proteins (or transcripts) compared to a reference. So a reduction to 1/10th in the number of transcripts is a 1-log reduction, to 1/100th is a 2-log reduction, and so on. A complete cytogenetic response (CCyR) roughly corresponds to a 2-log reduction. A “deep molecular response” is a 4-log reduction or better.
A deep molecular response means that your leukemia activity is profoundly suppressed. One benefit of this level of response is that a person who sustains a 4-log response may be able to enter a trial in which treatment is stopped, and no further medication will be needed.
But does a deep response confer any other benefits?
This issue was examined in 522 people treated for at least two years (Hu and colleagues. ASCO 2016; abstract 7057). Overall, 60% of people were able to achieve better than a 4-log reduction over an 8-9 year period. The median time to reach a deep response was 18 months.
People who had a sustained deep molecular response experienced fewer relapses, and were less likely to develop progressive CML. There was also a trend to improved long-term survival.
In reaching this important milestone, it didn’t appear to matter which path was taken. However, a higher proportion of people (about two-thirds) achieved a deep molecular response if they started treatment with Tasigna or Sprycel medication. Those who were treated with Gleevec (38%) or Iclusig (45%) were less likely to achieve their goal.