FDA staff questions data on leukemia drug

By Lisa Richwine

WASHINGTON (Reuters) - U.S. drug reviewers questioned whether a proposed leukemia drug from GlaxoSmithKline PLC and Genmab provides enough benefit to warrant approval, documents released on Wednesday said.

Shares of Danish biotech company Genmab fell 17.5 percent in Copenhagen, while shares of much larger Glaxo gained 0.9 percent on the New York Stock Exchange.

Food and Drug Administration staff said the magnitude of anti-cancer activity from the drug, Arzerra, was "difficult to quantify" in tests of patients with chronic lymphocytic leukemia, a common type of blood cancer in adults.

"The major issue regarding this application is whether the effect sizes ... are reasonably likely to predict clinical benefit," FDA staff said in a memo prepared for an FDA advisory panel that meets Friday.

The FDA will ask the panel for input on the companies' data. The agency usually follows panel recommendations when deciding whether to approve a drug, but does not have to.

Analysts believe annual sales of Arzerra could eventually top $2 billion, although the drug is unlikely to reach its full potential until the middle of the next decade. The makers are studying larger populations beyond CLL.

Initially, the companies are seeking approval for CLL patients who have failed two other treatments -- fludarabine and alemtuzumab -- and others who have failed fludarabine and for whom alemtuzumab, sold by Genzyme as Campath, was inappropriate because of their bulky tumors.

FDA staff said Glaxo would need to conduct another study to support approval for the latter group.