THURSDAY, Feb. 17, 2005 (HealthDay News) -- For the first time, a vaccine therapy that harnesses the power of the body's own immune system is proving successful in the fight against metastatic prostate cancer.
Researchers say the compound, called APC8015 (Provenge), primes patients' immune systems to recognize and kill prostate cancer cells that have spread throughout the body.
In a trial of 127 men with advanced disease, patients given the vaccine, called Provenge, experienced an average 18 percent increase in survival, compared to those on a placebo, the scientists report.
"For those of us doing research into metastatic prostate cancer, it looks pretty great," said study co-researcher Dr. Celestia Higano, an assistant professor of medicine and urology at the University of Washington in Seattle.
"We prolonged survival -- that's great news. It's the first time we've seen it with a vaccine in prostate cancer," she added.
She and her colleagues presented the findings Thursday at this year's Multidisciplinary Prostate Cancer Symposium in Orlando, Fla.
Besides promising a potential boon to people struggling with prostate cancer, the therapy gives "proof of principle" to the idea that immune-based treatments can have a real impact on prostate cancer and other malignancies, experts said.
"There have been many failures with this kind of approach, and many have wondered if we shouldn't set the bar lower, somehow lower our expectations, and not hope for extended survival," said Dr. Bruce Roth, a prostate cancer researcher at Vanderbilt University in Nashville, Tenn.
"But these findings are saying, 'No, looking for a survival advantage is a valid endpoint to look at for these agents,'" he said.
When caught early, prostate cancer remains very curable. However, despite advances in early detection, the disease remains the second leading cancer killer of U.S. men, according to the American Cancer Society. Even among men who develop the disease while it is still confined to the prostate, between 30 percent to 40 percent will experience a recurrence in years to come, experts say.
Because prostate cells depend heavily on testosterone to grow, therapies that reduce levels of circulating testosterone are often the first course of action in men who experience a recurrence. However, prostate cancer cells gradually grow resistant to hormonal therapy, so relapse is almost inevitable. Until very recently, doctors could only offer patients palliative therapies once that relapse set in.
But just last year, one new chemotherapy agent -- docetaxel (Taxotere) -- was found to improve survival in patients with metastatic disease by an extra six months, on average.
Now, Higano and her colleagues say their vaccine may extend survival, too.
"The vaccine is composed of a person's own immune cells that have been isolated from the blood and then sensitized to prostatic acid phosphotase, which is found on 95 percent of prostate cancer cells," Higano explained. These cells "are then infused back into the patient."
Once inside the patient, these sensitized cells prime the patient's immune system to recognize and destroy prostate cancer cells roaming throughout the body, Higano said.
The Seattle study involved 127 men with cancer that had spread beyond the prostate and grown resistant to hormonal therapy. Eighty-two of the men received Provenge, while the other 45 received a placebo. The researchers tracked patient outcomes for three years.
The patients taking Provenge survived an average of 25.9 months, compared to 22 months for those not taking the vaccine. And by the three-year mark, 34 percent of those on Provenge remained alive, compared with just 11 percent in the placebo group.
"It's the first immunological therapy to have some efficacy against metastic prostate cancer, after years of trying," Roth said.
The side effects were minimal -- "some fever and shaking for a few days at the beginning of therapy, but that was transient," Higano said.
Both Higano and Roth stressed that neither Taxotere nor Provenge represents a "cure" for metastatic cancer, but they agree that both bring a measure of hope.
"Along with Taxotere, this is the second trial [in a year] where something has impacted on survival -- that's really exciting," Higano said.
She cautioned, however, that decisions by Provenge's developer, the Seattle-based biotech company Dendreon, as well as the U.S. Food and Drug Administration, will largely dictate how long it might take before the vaccine is available to patients everywhere.
"Hopefully, we're talking one to two years, though," she said.
In other news released Thursday at the symposium, a study by researchers at Brigham and Women's Hospital and the Harvard School of Pubic Health suggests that increased levels of vitamin D may help protect against prostate cancer.
Comparing Vitamin D levels in blood samples from more than 2,400 men, the Boston team found that men with high levels of two vitamin D metabolites, in combination, were at a 45 percent lower risk of developing prostate cancer, compared with men who had lower levels of these two metabolites or those who had a high level of only one metabolite.
"Our finding suggests that vitamin D plays an important protective role against prostate cancer," said lead investigator Dr. Haojie Li in a prepared statement. Vitamin D is best sourced through exposure to sunlight, or certain foods.
In a third study, also from Brigham and Women's Hospital, Dr. Jing Ma and colleagues report that obesity may increase risks for death from prostate cancer. They found that, even after adjusting for other risk factors, statistically obese men with a body mass index (BMI) of 30 or above were twice as likely to die of the disease than normal weight men.
According to the researchers, obesity also doubled the risk of being diagnosed with metastatic prostate cancer -- 19 percent among obese men vs. 8 percent among normal-weight men.
"There are two possible explanations for these findings," Ma said in a prepared statement. "First, that being obese may delay the diagnosis of prostate cancer, or second, that being overweight or obese is associated with a biologically more aggressive form of prostate cancer."
More information
To learn more about detecting and treating prostate cancer, visit the American Cancer Society.
