NEW YORK, July 6 (Xinhua) -- The U.S. Food and Drug Administration (FDA)'s decision to delay approving an experimental therapy to treat prostate cancer has enraged seriously ill patients and triggered a bitter debate in the country, The Washington Post reported Friday.

    The first-of-its-kind therapy, called Provenge, is a "vaccine" designed to extend the lives of patients with advanced prostate cancer by stimulating their immune systems.

    A panel of experts recommended in March that the FDA approve Provenge. But in May, the agency instead asked for more evidence that the vaccine works after specialists, including Howard I. Scher of the Memorial Sloan-Kettering Cancer Center and Maha Hussain of the University of Michigan, questioned its effectiveness.

    Scher and Hussain told the FDA that Dendreon Corp., the small Seattle biotech company that developed Provenge, submitted a study to win approval for the drug that was so small that the apparent benefit it showed could have been the result of chance.

    The two experts then began receiving anonymous e-mails, phone calls and letters attacking and sometimes threatening them.

    Patients and advocacy groups staged a Capitol Hill rally on June 4, and demanded and got a meeting with FDA Commissioner Andrew C. von Eschenbach the same day. They began lobbying to amend FDA legislation moving through Congress to allow easier access to experimental treatments. But the FDA insisted that additional scientific data is required.

    The Provenge controversy comes amid revelations that a widely used diabetes drug, Avandia, may increase the risk of heart attacks. That triggered a similarly intense debate, including angry criticism of cardiologist Steven Nissen of the Cleveland Clinic, who sounded the alarm about the drug.

    People were divided over the issue, with some saying that FDA needs to be more vigilant while others believe the process is too long a wait.