Biotech company

Dendreon

(DNDN)

warned Friday that an interim analysis of a late-stage test of its prostate cancer vaccine didn't give much hope for success.

Shares of the Seattle-based firm closed Thursday at $8.05 per share, but were down $3.09, or 38.4%, in recent trading Friday.

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Dendreon is developing the vaccine, called Provenge, as a treatment for men with advanced-stage prostate cancer. But an independent analysis of the first of its late-stage tests -- designed to prove the vaccine's efficacy -- came back inconclusive.

"This preliminary analysis is inconclusive and does not provide a sufficient basis upon which to make definitive business decisions relating to the ongoing development of Provenge, as had been the purpose of the interim analysis," said Dendreon CEO Chris Henney, in a statement.

"It does indicate to us that it is possible, but not probable, that the primary endpoint of the study will be achieved," he added. "We look forward to a more detailed final analysis, which is anticipated to be conducted in mid-2002 when availability of the additional data required for the final analysis is expected."

Dendreon is conducting three late-stage tests of Provenge on men with various forms of prostate cancer. The company said it may have to conduct additional tests of the vaccines before it tries to file for marketing approval with the Food and Drug Administration.

The goal of developing a vaccine to treat cancer has been an elusive one, almost as difficult a feat as coming up with a vaccine for AIDS. The theory behind such a vaccine is that it can help the body's immune system recognize cancer cells as something foreign, or bad, in the body. Once a patient's immune system targeted cancer cells as foreign, it would attack and kill the cells. But to date, multiple efforts to develop such a cancer vaccine have not worked effectively enough.