MATTHEW PERRONE AP Business Writer WASHINGTON (AP) — Federal regulators on Friday questioned whether Genzyme’s leukemia drug Clolar should be approved for older patients based on limited studies conducted by the biotech drugmaker. Cambridge, Mass.-based Genzyme has asked the Food and Drug Administration to approve its injectable drug 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, 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 told the company in a 2007 meeting that a so-called randomized, controlled study would likely be needed to win approval. “It will be difficult to interpret the results of this trial without a control; we recommend that you conduct a randomized controlled study,” according to minutes from the meeting. Washington Analysis analyst Ira Loss said the agency’s negative comments “cast serious doubt on the approvability of this product for the proposed indication.” The FDA noted that a similar drug application from Johnson & Johnson — which also lacked a randomized study — was rejected by the agency’s panel of outside cancer experts in 2005. The FDA will ask the panel to weigh in on the drug on Tuesday. The agency is not required to follow the group’s advice, though it usually does. The panelists will be asked whether Genzyme correctly identified a group of patients who would not be suitable for chemotherapy. In its review, FDA scientists estimated 25 to 41 percent of the patients studied by the company may have been candidates for chemotherapy. In a separate posting online, Genzyme highlighted the positive results with its drug, saying 46 percent of patients in its 112-patient study saw remission of their cancer, usually after one treatment cycle. “Currently available therapy remains insufficient for these patients, creating a need for new treatments,” the company said.