Therapeutic cancer vaccines received a potentially big boost this week when Seattle-based biotech company Dendreon announced that its Provenge vaccine prolonged the lives of prostate cancer patients. The success of this trial could pave the way for approval of the drug, which triggers the body's immune system to attack malignant prostate tumors.

Most people think of a vaccine as a jab to prevent the winter flu and other viruses like polio or smallpox. Such vaccines often inject a piece of a virus into the body to trigger it to produce antibodies against it to ward off future infections. A new generation of vaccines can protect girls and young women from a virus that precipitates cervical cancers.

At the same time, scientists have labored for years on a wholly different approach like the Provenge vaccine that recruits immune molecules to treat cancers instead of preventing them. The theory is that such vaccines might be less toxic and more successful than other cancer treatments such as chemotherapy and radiation.

Dendreon officials said they would not reveal specifics of its Provenge trial until an American Urological Association meeting later this month. The lack of details left analysts scratching their heads and wondering if the results might be flawed.

According to Dendreon, 500-plus men with late-stage prostate cancer that had spread to other organs and who no longer received any benefit from other therapies participated in the trial. The pharma execs did not say how many of the patients benefited or how much longer those on the med lived than those who did not receive it. In an earlier trial, men treated with Provenge lived 25.9 months, compared to the 21.4 months of those who received a placebo.

Cancer-patient advocates have criticized the Food and Drug Administration (FDA) for being slow to approve Provenge; an FDA advisory panel two years ago recommended that the agency greenlight it. In fact, there has been such an outcry over the FDA's refusal to okay the med that two prostate cancer specialists who recommended against approval had to attend a conference with bodyguards, according to the New York Times.

Potential cancer vaccines have had a long-and checkered history, one in which Provenge has been a central player. The most recent results suggest that years of research may not be wasted. For more information, check out this profile of Dendreon that appeared in Scientific American magazine in 2004 as it was developing Provenge.

An immune system cell. Image Credit: Lawrence Berkeley National Laboratory