March 7 (Bloomberg) -- Amgen Inc. and Johnson & Johnson may face added restrictions on marketing anemia drugs to cancer patients as U.S. regulators weigh new studies showing the products raise the risk of tumor growth and death.

The U.S. Food and Drug Administration may advise doctors to stop prescribing Amgen's Aranesp and J&J's Procrit for patients with breast cancer, and possibly for all cancers, based on the latest findings, analysts said.

Amgen, the world's largest biotechnology company, lost $29 billion in market value last year after Aranesp, its top seller, and Epogen, another anemia drug, were tied to higher risks of heart attack, stroke and death at high doses. The FDA urged doctors a year ago to use the lowest doses possible after dangers were seen in patients with kidney disease and head and neck cancer. An advisory panel is scheduled to discuss the new studies next week.

``I don't know if it can get any worse,'' said Eric Schmidt, an analyst with Cowen & Co. in New York, in a telephone interview. ``It's reasonable to assume there will be more restrictions on the drugs' use.''

Amgen, based in Thousand Oaks, California, has lost 20 percent of its value since Dec. 6, when the drugmaker said it was in discussions with the FDA about new limits on the drugs. The decline reflects a worst-case assumption by investors that FDA limits will cost Amgen all U.S. sales of Aranesp for cancer patients, or about $1 billion a year in revenue, Schmidt said.

Aranesp, also used for kidney patients, generated $3.61 billion in worldwide sales in 2007, a 12 percent decline.

Advisory Panel

The FDA's advisory committee on cancer drugs is scheduled to meet March 13 in Gaithersburg, Maryland, to discuss the evidence of risk for cancer patients that has emerged since a panel last examined the drugs in May. The agency usually follows the recommendations of its outside advisers, although it isn't required to do so.

``We look forward to discussing the benefits and risks of the anemia drugs when used according to the product labeling,'' said Roy Baynes, Amgen's vice president of global development for oncology supportive care, in a telephone interview. J&J said in a Feb. 27 statement that a study showing increased risk of death across 51 clinical trials does ``not provide an accurate reflection of the safety profile'' of the anemia drugs.

Amgen fell 6 cents to $44.18 at 4 p.m. New York time in Nasdaq Stock Market composite trading. J&J, based in New Brunswick, New Jersey, dropped $1.12, or 1.8 percent, to $61.51 in New York Stock Exchange composite trading.

Amgen and J&J's anemia drugs are used to treat the weakness and fatigue of patients who have chronic kidney disease or are undergoing cancer chemotherapy. The medicines stimulate production of oxygen-carrying red blood cells.

4 Million Patients

More than 4 million patients have taken Amgen's anemia treatments since they were introduced, according to the company.

Epogen, used for patients on kidney dialysis, generated $2.49 billion in U.S. sales in 2007, down less than a percent from the prior year. Procrit, manufactured by Amgen and identical chemically to Epogen, is marketed by J&J in the U.S. under a license. Procrit had $1.69 billion in U.S. sales in 2007, an 18 percent drop from the previous year. It is sold for people with cancer and kidney patients not on dialysis.

New data on Aranesp's risks became public on Nov. 30, when Amgen issued a statement on a study called Prepare. It enrolled 733 breast cancer patients before they had surgery to remove tumors. All of the patients got chemotherapy. Of those who took high doses of Aranesp as well, 50 of 356 died, or 14 percent, compared with 37 of 377 patients, or 9.8 percent, among those who didn't take the anemia drug, Amgen said.

Cervical Cancer

Four days after disclosing the new breast cancer risks, Amgen told the FDA about a study of cervical cancer, called GOG- 191. That study also found a higher risk of death for patients on the anemia drugs, the FDA said in a notice on its Web site.

Researchers have been attempting to measure the risk across all studies. The analysis of 51 clinical trials over the past 20 years, published last month in the Journal of the American Medical Association, found that the anemia drugs raised the risk of death by about 10 percent.

Based on the new information, the FDA is likely to seek added warnings in the products' prescribing information, said Michael King, an analyst with Rodman & Renshaw in New York, in a note to clients March 3.

That alone may not hurt demand for the drugs, said King, who estimates there's a 30 percent chance the FDA panel will recommend ending the use of the anemia drugs for breast cancer patients, and a one-in-10 shot that the advisers will propose doctors stop prescribing the medicines for all cancer patients.

On March 12, a day before considering Amgen's anemia drugs, the same FDA panel will recommend whether to approve Nplate, the company's experimental drug to treat a blood-clotting disorder. The product may generate $117 million in 2009 sales, King said.

``If Amgen can make it though the panels with a recommendation for Nplate and emerge with Aranesp relatively unscathed, the stock could rally nicely from its currently depressed levels,'' King wrote to clients.

To contact the reporter on this story: Luke Timmerman in San Francisco at ltimmerman@bloomberg.net

Last Updated: March 7, 2008 16:20 EST