(Adds details, Roche quotes, previous dateline ZURICH)
By Ransdell Pierson and Toni Clarke
NEW YORK/BOSTON Feb 23 (Reuters) - Swiss drugmaker Roche Holding AG (ROG.VX) said on Friday it had suspended enrollment in a trial of an experimental anemia drug due to safety concerns, a setback analysts said could delay the drug's U.S. approval.
The news for Roche's drug, called Cera, deepens growing safety concerns over a class of blockbuster medicines that also includes Amgen Inc.'s (AMGN.O) Aranesp and Epogen, and Johnson & Johnson's (JNJ.N) Procrit and Eprex.
Roche said it is temporarily suspending recruitment into a mid-stage trial of Cera in anemic lung cancer patients because of an "imbalance" of deaths across the four arms of the study, which was conducted outside the United States.
The drugmaker did not reveal the number of deaths in each of the study arms, three of which involved patients receiving different doses of Cera and another that received Aranesp.
"We're not disclosing the numbers of deaths in the treatment arms because the study is continuing with patients already enrolled," said Roche spokeswoman Linda Dyson.
Sanford Bernstein biotech analyst Geoff Porges said Roche officials suggested overall mortality was higher than that seen in similar earlier trials, and that patients "were more debilitated" than in prior similar trials.
Cera, like its rivals, is a form of the natural protein erythropoietin, or EPO, which spurs the body to produce more red blood cells.
"We believe this event adds an additional black cloud to EPO drugs in cancer patients and may ultimately force physicians to become more cautious in their EPO use and payors to cut back on reimbursement," Jim Reddoch, an analyst with Friedman, Billings, Ramsey said in a research note.
Roche said the deaths were unrelated to the study drugs and there appeared to be no association of the events to excessive levels of hemoglobin, the protein in red blood cells that transports oxygen.
The company said the deaths were driven in part by the progression of the cancer.
EPO TUMOR LINK?
Some doctors have speculated EPO may feed tumors and help them grow, a possible explanation for higher death rates among EPO users in some recent cancer trials. Roche's Dyson declined to comment on the theory, or whether it was pertinent to the Cera study.
Amgen, the world's biggest biotechnology company, has been seeking to block Cera from entering the U.S. market and competing with its largest products. Aranesp alone generates annual sales of roughly $4 billion.
Roche has asked U.S. regulators to approve Cera -- under the brand name Mircera -- to treat anemia in patients with kidney disease. It may later seek approval to also market the drug for cancer patients that are anemic, if ongoing trials support that use.
Aranesp is approved to treat anemia in cancer as well as in patients undergoing dialysis -- meaning those with advanced kidney disease.
The news could prompt greater scrutiny by regulators of the safety of all EPO drugs, including Amgen's, especially when given in higher doses. But it may make it less likely that Cera will be approved by the U.S. Food and Drug Administration -- a potential boon to Amgen.
"Approving Cera has to have fallen a few notches on the FDA's to-do list," said Christopher Raymond, an analyst at R.W. Baird & Co. "This is unequivocally good news for Amgen."
Amgen executives were not immediately available for comment.
On Jan. 25 Amgen disclosed a higher risk of death among cancer patients not undergoing chemotherapy who were treated with Aranesp, compared with those receiving placebos.
The study involved patients with anemia and active cancer who were not receiving chemotherapy or radiation -- a group of seriously ill patients for whom Aranesp is not approved.
Amgen's setback last month comes on the heels of a study that cast a negative light on Procrit, a J&J form of EPO, and possible over-use of such medicines.
The FDA in November said it would review the study, which showed that kidney disease patients treated more aggressively with Procrit had a higher risk of cardiac complications and death.
Amgen shares closed down 51 cents to $66.23, while those of J&J slipped 26 cents to $64.15, both on the New York Stock Exchange. (Additional reporting by Sam Cage in Zurich)