Chronic-leukemia drug clears a big hurdle. (First-Line Treatment).

The cancer drug imatinib created a stir a few years ago when it rescued leukemia patients who had failed to improve on other treatments. Now, in the first large-scale test of the drug in people newly diagnosed with chronic myeloid leukemia (CML), imatinib has stopped or reversed the disease in nearly all patients receiving it.

These findings indicate that imatinib--originally called STI-571 and now marketed under the name Gleevec--ought to be formally approved as the first-line treatment for CML, says study coauthor Richard A. Larson of the University of Chicago. Currently, the Food and Drug Administration endorses imatinib only for CML patients who have failed on standard therapy, although many U.S. physicians prescribe it more widely, Larson says.

He presented the results before a packed hall at a meeting of the American Society of Hematology in Philadelphia this week.

Larson and a team of collaborators in 16 countries randomly assigned 1,106 CML patients to two groups, each of which received either a daily imatinib pill or a standard CML treatment--injections of interferon-alpha boosted with a compound called cytarabine. At least 18 months after the start of treatment, 97 percent of the patients getting imatinib were in leukemia remission, although only 5 percent were completely free of all cancer signs. Of the initial imatinib group, 86 percent were still taking the drug with few side effects at the end of 18 months, Larson says. In contrast, the interferon treatment proved effective and tolerable in only about 11 percent of the people originally assigned to receive it.

During the study, participants were given the option to switch to the other regimen if side effects became intolerable or their treatment wasn't working. In all, 58 percent of the interferon group switched to imatinib during the trial. Because of this change, Larson says, fewer than 10 percent of participants in the initial interferon group died. Only 2 percent of the original imatinib group switched to interferon treatment, he says.

These results "clearly show that imatinib is superior to interferon," comments Stephen MacKinnon of University College London Hospital. He notes, however, that some CML patients have another option--a bone marrow transplant. This procedure--if it works--is the only established way to cure CML, says MacKinnon. The rigorous treatment requires that a patient's marrow cells first be killed off and then replaced by healthy marrow from a donor, a procedure that carries severe risks.

Despite recent advances in transplant science, many patients and their doctors may nevertheless see imatinib as a lower-risk option than bone marrow transplant, MacKinnon says. Roughly 20,000 people in the United States have CML. The average age of contracting it is between 40 and 50 years.

Although imatinib appears highly promising, it has been studied for less than 5 years, cautions Ronald Hoffman of the University of Illinois College of Medicine in Chicago. Only long-term follow-up of patients in this and other studies will reveal whether the drug can keep CML at bay indefinitely and continue to spare patients the side effects that have plagued interferon therapy, Hoffman says.