Federal health advisers said anemia drugs sold by Amgen Inc. and Johnson & Johnson should only be used by a limited segment of chemotherapy patients - a restriction that could cost the companies millions. The limits, proposed Thursday by a Food and Drug Administration advisory panel, were the latest blow to three blockbuster medications already plagued by concerns over increased risks of death and tumor growth. The cancer experts overwhelmingly voted to keep the drugs on the market for chemotherapy patients, but said use should be limited to those with uncurable forms of cancer. The experts also voted nine-to-five to withdraw the drug's use in patients with breast or head-and-neck cancers, such as those affecting the sinuses, throat and lymph nodes.

FDA often follows its panelists' advice, though it is not required to do so. Agency staffers said they would begin considering the recommendations immediately, but set no timetable for action.

FDA's director for new drugs said the votes reflect the unresolved safety questions.

"It was clear from the discussion that they are concerned about the risks of these drugs, but the scope of those risks is not clear," John Jenkins said. "We don't have perfect data at this point."

The recommendation was not as restrictive as some on Wall Street had feared, and shares of Amgen climbed by nearly 5 percent in afternoon trading. Many analysts said the panel could have recommended halting the drugs' use in all chemotherapy patients, endangering as much as $1 billion in sales for Amgen.

FDA already bolstered warning labels on the treatments - Aranesp, Epogen and Procrit - three times in the past year. But the action recommended Thursday would go much further, effectively wiping out a large slice of the market for anemia drugs.

Amgen manufactures all three; New Brunswick, N.J.-based J&J sells Procrit.

Bear Stearns analyst Mark Schoenbaum estimated the restrictions could eliminate about 40 percent of the market for Amgen's best-seller Aranesp. Epogen is better insulated because it's used almost exclusively by kidney dialysis patients.

The two combined accounted for $6.2 billion, or more than 40 percent, of the Thousand Oaks, Calif.-based company's revenue last year. Procrit had sales of $2.9 billion, or less than 5 percent of J&J's total sales.

Earlier on Thursday FDA staff told panelists there is no definitive evidence that the blockbuster anemia drugs are safe when used as recommended.

Amgen and J&J argued Thursday that the safety problems cited by FDA have been inconsistently reported across dozens of studies. And they pointed out that only studies involving higher-than-recommended dosing levels showed significant safety risks.

Complicating the safety debate was the fact that the recommended dosing for the medications has changed in the last year. Until recently, many doctors would use high drug doses to raise patients' red blood cell levels to those of a healthy person, believing this improved quality of life.

But last year FDA cautioned doctors against that practice, saying they should only use the lowest levels possible.

Amgen and J&J outlined a large-scale study Thursday to try and answer whether anemia drugs hasten death and tumor growth when used according to the current label, but results won't be available for at least five years.

Until then, the companies proposed educational outreach to doctors.

Amgen and J&J argued that any risks of its drugs do not outweigh the alternative - giving patients regular blood transfusions.

However, FDA pointed out blood transfusions are safer now than two decades ago, when concerns over HIV in the national blood supply persuaded many doctors to prescribe anemia drugs.

The debate over whether the drugs are overused remains - and riled some panelists who questioned Amgen's promotional tactics.

Some cancer experts contend that the company's practice of discounting drugs for doctors who buy large quantities encourages overuse.

During the meeting, panelist Michael Perry pressed Amgen Vice President Joshua Ofman to find out if the company uses rebates and discounts to market anemia drugs. Ofman's response was long and complicated.

"You ought to be on 'Dancing with the Stars,'" said Perry, director of the Ellis Fischel Cancer Center. "You can't dance your way out of a yes or no question."

Ofman then confirmed that Amgen does offer rebates and discounts for doctors who purchase large amounts.

Shares of Amgen rose $2.19, or 4.9 percent, to close at $47.18. J&J's stock rose 26 cents to $62.81.