June 1, 2011 -- A vaccine that marshals the body's own defenses to recognize and kill cancer cells may shrink tumors and delay the progression of late-stage melanoma more effectively than conventional therapy alone, a new study shows.
"It's one of the first vaccine studies that has been positive in cancer," says study researcher Patrick Hwu, MD, chair of the department of melanoma medical oncology at the University of Texas M.D. Anderson Cancer Center in Houston. "It shows the principle that vaccines are important."
Vaccines, which are normally used to prevent infectious diseases, are a relatively new approach in cancer treatment, and very few have been able to show even modest benefits to patients in clinical trials.
In 2010, the FDA approved a vaccine for prostate cancer, called Provenge, after a study showed that men with advanced cancer who received the vaccine lived about four months longer than those taking a placebo.
Study researchers say the experimental melanoma vaccine probably also achieved a measure of success because it was used in combination with a therapy called interleukin 2 (IL-2).
After the vaccine primes the immune system to recognize and attack cancer cells, IL-2 sends a message to the immune system to make more soldiers to carry out the siege.
"It's a combination of the vaccine to stimulate the immune cells plus IL-2 to drive the proliferation of the immune cells," Hwu says.
Still, researchers are quick to acknowledge that this new approach is not a panacea. Just 16% of participants on the vaccine had their tumors shrink by at least 50%, the cutoff researchers used to determine a clinical response to the drug.
But that was more than twice the number of patients who saw a clinical response in the group that got a standard therapy alone.
On average, the group taking the vaccine saw the progression of their cancer delayed for about two weeks longer than those getting standard therapy alone.
And patients on the vaccine lived about six months longer than those on standard therapy alone, indicating that the experimental treatment may extend life, though researchers say that observation may be unreliable since their study wasn't designed to detect differences in survival between the two groups.