A U.S. advisory panel called for marketing restrictions on popular anemia drugs sold by Amgen and Johnson & Johnson.
Shares of both Amgen and J&J fell on the news.
The Food and Drug Administration panel of outside cancer experts urged the agency to make marketing of the medicines contingent upon further restrictions being placed on the drugs' labels and upon an agreement by the companies to conduct more clinical trials. The panel also voted for disease-specific labels on anemia drugs and lower dosages.
The FDA usually, but not always, follows the recommendations of its advisers.
Amgen's Aranesp and Epogen and J&J's Procrit had combined sales of about $10 billion in 2006.
Amgen contends that the benefits blood-cell boosting drugs, which allow cancer patients to have significantly fewer blood transfusions, outweigh the risks.
Health regulators have been concerned that the drug has been prescribed too aggressively and could be harming patients. The FDA imposed its strongest warning label on the drugs in March and advised physicians to use the lowest dose possible.
Aranesp had sales of about $4.1 billion last year, and along with its predecessor Epogen accounted for roughly half of Amgen's sales.
In April, Amgen said data from a recent study of Aranesp and lung cancer patients showed no difference in the risk of death compared with a placebo.
The drugs are forms of the natural protein erythropoietin, or EPO, used to treat anemia by stimulating the body's production of hemoglobin, the protein in red blood cells that carries oxygen.