ASCOIn a phase III study, imatinib(Drug information on imatinib) mesylate (Gleevec), formerly known as STI571, produced a 96% complete hematologic response rate and a 68% complete cytogenetic response rate in newly diagnosed chronic myeloid leukemia (CML) patients, Brian Druker, MD, said on behalf of the IRIS (International Randomized Interferon vs STI-571) Study Group at the 38th Annual Meeting of the American Society of Clinical Oncology (abstract 1).
"This study shows that with the right target and the right drug, you can see remarkable results," Dr. Druker said at a media briefing announcing the results. Imatinib mesylate, a specific inhibitor of the Bcr-Abl tyrosine kinase, has previously been proved effective in CML in advanced stages and in patients who no longer respond to interferon.
From June 2000 to January 2001, the IRIS study enrolled 1,106 patients at 177 centers in 16 countries. The patients, all within 6 months of diagnosis and in chronic phase, were randomized to receive imatinib 400 mg/d or interferon at a target dose of 5 MIU/m²/d plus cytarabine(Drug information on cytarabine) arabinoside (ara-C) at a dose of 20 mg/m²/d for 10 days per month.
Crossover was allowed for lack of response, loss of response, a rapidly increasing white blood cell count, or severe intolerance of therapy. Median follow-up was 14 months.
"We were astounded by how much better the Gleevec patients did," said Dr. Druker, professor of medicine, Oregon Health & Science University. In contrast to the 96% complete hematologic response rate seen with imatinib mesylate, the interferon patients had a rate of 67%.
The imatinib mesylate patients had an 83% major cytogenetic response rate (68% complete), compared with only 20% for the interferon/cytarabine group (7% complete).
In addition, 23% of patients in the interferon group could not tolerate the therapy, compared with 0.7% of patients who were intolerant to imatinib mesylate.