UPDATE 4-Roche suspends enrollment in anemia drug trial

(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.