In patients with chronic myeloid leukemia (CML), the safety and benefits of imatinib persisted over the course of 10 years in a follow-up study reported online March 9 in the New England Journal of Medicine.

The initial results of the phase III International Randomized Study of Interferon and ST1571 (IRIS) trial “fundamentally changed CML treatment and led to marked improvements in prognosis for patients” when imatinib was shown more effective than interferon plus cytarabine among newly diagnosed patients in the chronic phase of the disease, said Andreas Hochhaus, MD, of the Klinik für Innere Medizin II, Universitätsklinikum Jena (Germany), and his associates. The researchers are now reporting the final follow-up results after a median of 10.9 years for the 553 patients who had been randomly assigned to receive daily oral imatinib in the IRIS trial.

The estimated rate of event-free 10-year survival was 79.6% with imatinib. In comparison, the estimated event-free 10-year survival was 56.6% among patients assigned to interferon plus cytarabine.

The high rate of crossover to the imatinib group among IRIS study participants precluded a direct comparison of overall survival between the two study groups at 10 years. However, the estimated overall 10-year survival in the imatinib group alone was 83.3%. “A total of 260 patients (47.0%) were alive and still receiving study treatment at 10 years, 96 patients (17.4%) were alive and not receiving study treatment, 86 known deaths (15.6% of patients) had occurred, and 11 patients (20.1%) had unknown survival status,” Dr. Hochhaus and his associates reported (N Engl J Med. 2017 Mar 9. doi: 10.1056/NEJMoa1609324 ).

Approximately 9% of those in the imatinib group had a serious adverse event during follow-up, including 4 patients (0.7%) in whom the event was considered to be related to the drug. Most occurred during the first year of treatment and declined over time. No new safety signals were observed after the 5-year follow-up.

“These results highlight the safety and efficacy of imatinib therapy, with a clear improvement over the outcomes that were expected n patients who received a diagnosis of CML before the introduction of tyrosine kinase inhibitor therapy, when interferon alfa and hematopoietic stem-cell transplantation were the standard therapies,” the investigators said.

Second-generation tyrosine kinase inhibitors have been developed since the IRIS trial was begun, and “it remains to be seen whether they will have similarly favorable long-term safety. Given the long-term safety and efficacy results with imatinib and the increasing availability of generic imatinib, comparative analyses evaluating the available tyrosine kinase inhibitors for first-line therapy are likely to be forthcoming,” they noted.