MATTHEW PERRONE AP Business Writer WASHINGTON (AP) — A panel of cancer experts has issued a negative review of a leukemia drug from Genzyme, saying more data is needed to establish its safety and efficacy for older patients. The Food and Drug Administration's oncology panel voted 9-3 Tuesday that Cambridge, Mass.-based Genzyme should be required to conduct a larger, comparison study to prove its drug is safe and effective. Clolar already is approved for a form leukemia in patients younger than 21. Genzyme is seeking approval for adults with leukemia who are older than 60, but are not healthy enough to undergo chemotherapy. Leukemia is a cancer of the blood or bone marrow. The FDA asked Genzyme to conduct a randomized controlled study, which compares patients taking the drug to those taking alternative treatments. Such studies are commonly used to gauge a drug's effect. However, Genzyme never conducted the study, saying doctors were unwilling to put cancer patients on the alternative treatment recommended by the FDA. Panelists complained that without a comparison it was difficult to say whether patients would truly do better taking Clolar than drugs already in use. "It is unclear what group of folks would benefit most from this drug," said Dr. Wyndham Wilson, of the National Cancer Institute. "In the absence of that I would not want to see a change in standards without a randomized study." Genzyme researchers said it was too soon to decide whether the company would go back and conduct the recommended trial. Genzyme Vice President Dr. Mark Hayes noted that the FDA has pushed back the deadline for making a decision on Clolar — from September to December — giving the company more time to work with regulators. "We have further opportunity to engage the FDA about this population and the other issues discussed at the meeting," Hayes told reporters. During Tuesday's meeting, Genzyme emphasized positive results from a relatively small, 112-patient study of its drug. About 46 percent of patients experienced remission of their cancer, and only 10 percent died within a month of the study's launch — a relatively small percentage. "I agree there is definitive evidence of activity," said panel chair Dr. Gail Eckhardt of the University of Colorado. However, the company's data were not strong enough to overcome concerns about the design of its study. FDA reviewers said it was unclear whether the patients selected by Genzyme were truly too frail to undergo chemotherapy treatment. The FDA said between 25 and 41 percent of patients may have been healthy enough to take standard chemotherapy, calling into question the drug's true benefit.