THURSDAY, June 29 (HealthDay News) -- U.S. regulators gave accelerated approval Wednesday to a new targeted therapy to treat people with chronic myeloid leukemia (CML).

The drug, Sprycel (generic name dasatinib), was also given regular approval to treat adults with Philadelphia chromosome-positive acute lymphoblastic leukemia (ALL), a more serious form of leukemia.

The approvals are only for patients who are resistant or intolerant to other therapies, including Gleevec (imatinib), now considered the gold-standard drug therapy for these conditions.

The arrival of Sprycel, which was developed by drug maker Bristol-Myers Squibb, solidifies an era of targeted molecular therapies for conditions such as CML.

"Gleevec is the poster child for targeted therapies and this approval represents a continued interest in looking into and changing the therapy for this disease," Dr. Richard Pazdur, director of the Office of Oncology Drug Products at the U.S. Food and Drug Administration's Center for Drug Evaluation and Research, said at a press conference Thursday. "Prior to 2001, one of the only major drugs available was interferon, which was a very toxic drug with very poor responses and minimal impact."

"These targeted therapies really represent major advances, both in initial treatment of the disease (with Gleevec) and those with refractory disease with Sprycel," Pazdur continued. "We're seeing continued interest to continue the progress that we've seen."

Targeted or molecular therapies such as Gleevec and Sprycel are very specific in the way they work, delivering maximal treatment impact with minimal side effects.

Wednesday's Sprycel approvals were based on evidence from four studies involving more than 400 patients who had stopped responding or were intolerant to Gleevec.

Almost half (45 percent) of patients with the earliest stage of CML (chronic phase) had a response to Sprycel. Response was defined as the proportion of patients who had no detectable leukemia cells or a significant reduction in leukemia cells.

In patients with advanced phases of CML and for those with Philadelphia-chromosome-positive ALL, response rates ranged from 31 percent to 9 percent. Most of the patients who had a response maintained that response after six months. The Philadelphia chromosome is a genetic abnormality characteristic of this condition.

Sprycel did produce side effects, including diarrhea, nausea, fever, headache, fluid retention and even hemorrhaging.

Studies are continuing to see if the improved white blood cell counts seen in these patients ultimately translate into improved survival or improvement in leukemia-related symptoms.

"We're looking at the maturation of clinical trial data," Pazdur said.

CML, a rare cancer marked by the uncontrolled growth of white blood cells, affects about 4,600 people every year in the United States.

By all accounts, the success rate of Gleevec has been astounding. Data presented at this month's meeting of the American Society of Clinical Oncologists showed that overall five-year survival for people with CML on the drug was 89 percent (95 percent if only deaths related to CML were considered). At the same time, 93 percent of patients taking the drug had still not progressed from the chronic to the acute phase of the illness.

But while the relapse rate for Gleevec in newly diagnosed patients taking it as front-line therapy is low -- about 4 percent per year -- patients who started on a different drug before getting Gleevec tend to relapse earlier, the researchers found. Not everyone will benefit indefinitely.

"Gleevec is great, there's no question," said Dr. Charles L. Sawyers, senior author of a Sprycel trial and an investigator with the Howard Hughes Medical Institute at the University of California, Los Angeles' Jonsson Cancer Center, at the time. "There is a reason to have a second drug, and the second drug [Sprycel] looks good."

An FDA advisory panel recommended approval of Sprycel in early June. And scientists presenting research earlier this month at the annual meeting of the American Society of Clinical Oncologists predicted that approval would come in as little as two weeks.

More information

Visit the Leukemia and Lymphoma Society for more on CML.