>GERN - myelosuppression
Just talking from general principles here, if you have a drug that inhibits mutated progenitor cells, then a lot will depend on what the patient has left in the way of non-mutated progenitor cells. If those are few and far between, then you are going to see a lot of myelosuppression.
So it is plausible that some of these hematological safety issues would not be nearly as severe if you treat earlier in the disease, before the patients have been through the mill.
Peter