The treatment kept the disease in check for 37 months compared with 13.5 months for those who didn't get the drug, according to research reported Sunday at the American Society of Hematology meeting in Atlanta. The 414 patients in the study had advanced disease and were initially treated with chemotherapy.

The findings may spur wider use of the drug, limited because of Zevalin's high cost and the reluctance of Medicare, the U.S. health insurance program for the elderly and disabled, to pay for it. Medicare reimbursement typically covers less than the cost of the drug, meaning many patients are denied access to the treatment, researchers said.

"This is a one-shot deal, and it's expensive, but it works," said Gary Dillehay, a radiology professor at Northwestern Memorial Hospital in Chicago, in a phone interview. "It's also a loss leader.