Dendreon's Prostate Vaccine Validated with Drama

Dendreon (DNDN) appears to have defied the many skeptics of its controversial experimental prostate cancer vaccine, Provenge. The drug extended survival in patients in the last stages of the disease by a median of 4.1 months, according to a the results of a clinical trial presented on Apr. 28—a month longer than Taxotere, a harsh chemotherapy that is currently the only drug for advanced prostate cancer.

The study of 512 men also found that 31.7% of the patients on Provenge were still alive at the three-year mark, compared with 23% of those on a placebo. Side effects from Provenge were minimal, although four men did develop non-fatal blood clots.

Although far from a cure, the drug represents the first significant progress in more than a decade against advanced prostate cancer, which kills some 30,000 men in the U.S. each year. For very sick patients, any additional survival time is considered a breakthrough by cancer specialists; the 4.1 months of added survival time represent a median, meaning that half the patients on the drug lived longer than four months and the other half lived less. As such, Provenge has won praise from doctors and patients alike. "Hundreds of thousands of men fighting prostate cancer will now have real hope that a safe and effective new option will be available to them in their fight for life," said Scott Riccio, executive director of the cancer patient advocacy group Accelerate Progress.

Dendreon's stock, however, suffered a nasty and unexplained blow in a couple of minutes before trading was halted on the Nasdaq exchange ahead of the announcement of the trial results. Between 1:25 p.m. and 1:27 p.m., the stock price fell 69%, to 11.81, at which point trading was stopped. The Nasdaq initially thought a broker's error was to blame for the drop, but later announced the stock trades would stand, according to Bloomberg. The shares more than doubled when trading resumed after hours.

first cancer vaccine to extend life

The stock slide was a marked reversal of what happened earlier this month, when Dendreon shares tripled in value on Apr. 14 after initial reports of the successful trial were announced. Short sellers had bet heavily against Dendreon.

Provenge is the first cancer vaccine to prove in a clinical trial that it can keep patients alive longer. For decades, scientists have been trying to develop such a vaccine, meant to activate the body's own immune system to attack tumors, with little success. The Provenge trial "validates the long-standing but elusive aspiration to harness a patient's own immune system to fight cancer," said Dr. Philip Kantoff, head of the prostate cancer program at Dana-Farber Cancer Institute in Boston and a principal investigator of the trial.

Dendreon CEO Dr. Mitchell Gold couldn't help but gloat a little over the results, released almost exactly two years after the Food & Drug Administration, in a much-debated decision, rejected the company's application for Provenge.

A panel of experts convened by the FDA had voted 17 to 2 to approve the drug, despite inconclusive evidence that it was effective. But the FDA rejected their recommendation, leading to a firestorm of protest from prostate cancer patients and Dendreon investors. The company set off on a larger trial designed to prove that the drug could extend survival.

customized for each patient

Ever since Gold announced two weeks ago that results met FDA requirements, the Seattle-based company has displayed a huge banner on the entire front of its headquarters that says: "Congratulations Dendreon. Global Impact Starts Here." And in releasing the full results Tuesday at the American Urological Assn. meeting in Chicago, Gold said they "confirm the potential for Provenge in prostate cancer and validate the potential of our pipeline."

Gold has said the company will reapply for FDA approval by the end of this year.

Experts say he has reason to be confident of approval, since Provenge seems to be both safe and more effective than Taxotere. The Provenge results are considered statistically significant because the trial had a so-called "p-value" of 0.032—meaning the odds were less than 3.2% that the outcome resulted from chance. The FDA traditionally will not consider a drug with a p-value of more than 5%.

The FDA is expected to closely monitor Provenge's complex manufacturing process, however. The drug must be customized to each patient: Blood cells are collected from the patient and mixed with a protein found on prostate cancer cells and a vector designed to stimulate the immune system. The resulting drug is given as a one-time treatment, delivered by infusion three times over two weeks. Ideally it will alert the immune system to attack the prostate tumor while leaving healthy tissue alone.

That process probably guarantees the drug will be costly, though the company has not disclosed pricing details. If the drug is approved, analysts expect it will bring in more than $1 billion in annual revenues within a few years.

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