WASHINGTON (AP) — A panel of cancer experts will debate Tuesday whether a leukemia drug from Genzyme should be approved for older patients, despite several limitations of the company's studies. Cambridge, Mass.-based Genzyme has asked the Food and Drug Administration to approve its injectable drug Clolar for adults older than 60, who have leukemia but are not healthy enough to undergo chemotherapy. Leukemia is a cancer of the blood or bone marrow. Clolar already is approved for a form of the disease called acute lymphoblastic leukemia in patients younger than 21 years old. But in briefing documents posted online last week, FDA reviewers complained about several problems with the company's study. Primarily, that Genzyme did not compare patients taking the drug to those taking a sham treatment, a practice commonly used to gauge a drug's effect. The FDA will ask its panel of outside oncologists to vote on the company's drug Tuesday. The agency does not have to follow the group's advice, though it often does. Washington Analysis analyst Ira Loss said the agency's negative comments "cast serious doubt on the approvability of this product for the proposed indication." In a separate posting online last week, Genzyme highlighted the positive results with its drug, saying 46 percent of patients in its 112-patient study experienced remission of their cancer, usually after one treatment cycle.