Patients with Chronic Myelogenous Leukemia Continue to Do Well on Imatinib at 5-Year Follow-Up

Paula Moyer, MA

June 12, 2006

June 12, 2006 (Atlanta) -- Patients with chronic myelogenous leukemia (CML) continue to have high rates of progression-free and overall survival even after 5 years of treatment with imatinib ( Gleevec, Novartis), according to a group of investigators that presented its findings here at the 42nd annual meeting of the American Society of Clinical Oncology.

"Our hope is that patients can stay on imatinib for an indefinite period of time," said principal investigator Brian J. Druker, MD, at a briefing. "Although it does not completely eradicate the presence of CML, we're gaining confidence that patients will continue to do well and that their futures are really quite hopeful." Dr. Druker is a professor of medicine at Oregon Health Sciences University in Portland.

The findings from the 5-year follow-up study of the International Randomized Study of Interferon plus Ara-C vs STI571 in Chronic Myeloid Leukemia (IRIS) study were presented by Dr. Druker on behalf of the IRIS study group.

Investigators conducted the long-term study after a phase 3 study had found that imatinib was superior to the interferon cocktail in 1106 patients newly diagnosed with CML in chronic phase. As a result of those findings, the investigators allowed patients in the control group to switch to imatinib, and they then followed them for 5 years. The investigators used the following criteria to assess treatment:

  • Complete hematologic response.

  • Complete or partial cytogenetic response, which they defined respectively as 0% and 1% to 35% metaphases, respectively.

  • Major cytogenetic response, the sum of complete and partial responses.

  • Major molecular response, or more than 3 log reductions of BCR-ABL transcript levels from the standardized baseline.

  • Time to progression, defined as a loss of hematologic or cytogenetic response.

  • Evolution to either accelerated phase or blast crisis.

  • Death due to any cause during treatment.

  • Overall survival.

After a median follow-up of 54 months, 72% of the 553 patients who were initially randomized to imatinib remain on treatment, Dr. Druker said. He noted that 5% had discontinued due to adverse events and 9.5% had dropped out due to an unsatisfactory therapeutic effect, while 11% had discontinued due to other reasons and another 2.5% had crossed over to the interferon regimen.

The cumulative best response rate for a complete hematologic response was 97%, while 88% of patients had had a major cytogenetic response and 82% had had a complete cytogenetic response. The overall survival rate was 90%, and that rate was increased to 93% when bone marrow-transplant patients were excluded.

The vast majority, 84%, had not progressed while on treatment, and 93% had been free from accelerated phase or blast crisis episodes. The annual rate of progression to accelerated phase or blast crisis had been less than 1% in the fourth year, a rate that was itself lower than each of the previous 3 years, for which such rates were 1.5%, 2.8%, and 1.6%, respectively.

Of the 436 patients with a major cytogenetic response at 12 months, nearly all, 96%, were free of progression to the accelerated phase or blast crisis at 54 months. Of those who did not have such a response at 12 months, 81% were free from these events ( P <0.001 compared with responders). Further, no patient with a major molecular response in the first 12 months had this type of progression within the follow-up period.

"These long-term results are very encouraging," said Peter Ravdin, MD, who was not involved in the study. "They show that, if you had a major response initially, the benefit was extremely durable." Dr. Ravdin is a clinical professor of oncology at the University of Texas Health Science Center in San Antonio.

He added that the findings may obviate earlier concerns about high-dose therapy with stem-cell support. With the broadened options that imatinib provides, "now it [stem-cell support] will be rarely used," he said. "This study confirms all of the early results and shows that this drug may be given successfully to people over the long term."

ASCO 42nd Annual Meeting: Abstract 6506. Presented June 3, 2006.


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