Report from the American Society of Clinical Oncology (ASCO), Chicago IL, May 29-June 2, 2015
When starting treatment with a TKI, achieving an early response to medication bodes well for future success. If a medication can suppress leukemia cells quickly, it’s less likely that other mutations will emerge. The analogy is a fire: it’s better to douse the flames completely rather than allow a few embers to keep smouldering.
The current benchmark is to reduce the number of BCR-ABL transcripts to less than 10% (i.e. a 1-log reduction) within the first three months of treatment (Baccarani and colleagues. Ann Hematol 2015;94 Suppl 2:S141-S147). Then it’s important to reach a 2-log reduction by six months, and a 3-log reduction within the first year. If any of these milestones isn’t reached, it suggests that the drug isn’t working well enough and you may need a different medication to control your CML.
A new study has looked at whether there are even earlier indicators of treatment success or failure (Malhotra and colleagues. ASCO 2015; abstract e18038). The marker they used was complete hematologic response (CHR, i.e. normalization of your blood cell counts). The numbers of blood cells are abnormal in CML, but are the first thing that shows a response when you start taking a TKI. So a response in the blood is the initial stepping stone to a response at the cellular or molecular level.
Here again, speed was of the essence. Among those achieving CHR within the first 6 weeks, 89% went on to achieve the 3-month milestone of a 1-log molecular response. If it took 6-12 weeks to achieve CHR, the likelihood of a 1-log reduction at three months went down to 75%.
So “CHR velocity” may provide the earliest indication that treatment is on track. However, these results will need to be confirmed in additional studies.