For this study, researchers defined disease progression as blood counts no longer being controlled by Gleevec, loss of a cytogenetic response, advancement to accelerated phase or blast crisis, or death during treatment.
Researchers found that achieving a complete cytogenetic response, which refers to the Philadelphia chromosome disappearing altogether from a patient's blood cells, had a significant impact on a patient's long-term outcome regardless of when it occurred in treatment. Patients whose cytogenetic response was complete were least likely to experience disease progression.
Interestingly, the length of treatment needed to reach a complete response had no effect on survival. Survival without disease progression at 24 months was 96 percent for patients with a complete response within the first three to six months, and 93 percent for those who achieved a complete response only after six months.
Researchers also looked at which patients were likely to have a complete response to Gleevec. Patients who were 35 percent Philadelphia chromosome positive or less at any time during treatment often had a complete response. Patients who were greater than 95 percent Philadelphia chromosome positive at three months still had nearly a 50 percent chance of subsequently obtaining a complete response. However, patients who were greater than 95 percent Philadelphia chromosome positive after six months or more of therapy had no more than a 14 percent chance of achieving a complete response.
Thus, three months is too soon to judge a response to Gleevec. On the other hand, patients who are greater than 95 percent Philadelphia chromosome positive at six months may be candidates for other treatment options.