Vaccine Therapy for Prostate Cancer Advances
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, according to a report at the Multidisciplinary Prostate Cancer Symposium.
Researchers say the compound, called APC8015 (Provenge®), primes patients' immune systems to recognize and kill prostate cancer cells that have spread throughout the body.
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 say.
"For those of us doing research into metastatic prostate cancer, it looks pretty great," says study co-researcher Dr. Celestia Higano, an assistant professor at the University of Washington in Seattle.
"We prolonged survival - that's great news," Dr. Higano says. "It's the first time we've seen it with a vaccine in prostate cancer."
Prostate cancer is the most common cancer, excluding skin cancers, in American men. The American Cancer Society (ACS) estimates that during 2005 about 232,090 new cases of prostate cancer will be diagnosed in the US. About one man in six will be diagnosed with prostate cancer during his lifetime, but only one man in 33 will die of this disease.
According to the Prostate Cancer Foundation (PCF), no single cause of prostate cancer has been identified. There are likely a variety of causes and contributing factors that lead to prostate cancer. The major known risk factors for prostate cancer are age, race, and family history. Although there are no conclusive data, diet and other environmental factors may play a role as well, states the PCF.
Regarding cancer vaccines, Dr. Bruce Roth, a prostate cancer researcher at Vanderbilt University, says, "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.
"But these findings are saying, 'No, looking for a survival advantage is a valid endpoint to look at for these agents,'" he notes.
When caught early, prostate cancer remains very curable.
However, despite advances in early detection, the disease remains the second leading cause of cancer death for men in the US, according to the ACS.
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, physicians 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, Dr. 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 phosphatase, which is found on 95 percent of prostate cancer cells," Dr. Higano explains. 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, Dr. Higano says.
In a trial of 127 men with advanced disease, patients given the vaccine experienced an average 18 percent increase in survival, compared to those on a placebo (an inactive substance), the scientists report.
The Seattle study involved 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 metastatic prostate cancer, after years of trying," Dr. Roth says.
The side effects were minimal - "some fever and shaking for a few days at the beginning of therapy, but that was transient," Dr. Higano explains.
Both Drs. Higano and Roth stress 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," Dr. Higano says.
She cautions, however, that decisions by Provenge's developer, the Seattle-based biotech company Dendreon, as well as the US 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 says.
Always consult your physician for more information.
|
In other news released at the Multidisciplinary Prostate Cancer 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.
The study compared 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," says lead investigator Dr. Haojie Li. The best sources of vitamin D are 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 versus 8 percent among normal-weight men.
"There are two possible explanations for these findings," Dr. Ma says.
"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," notes Dr. Ma.
Always consult your physician for more information.
|
