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.
How the Vaccine Works
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.
The study is published in the New England Journal of Medicine.
"This is a first vaccine study in melanoma that really shows an effect. This is fascinating," says Arkadiusz Dudek, MD, PhD, associate professor of medicine at the University of Minnesota's Masonic Cancer Center in Minneapolis.
Dudek recently reviewed the clinical evidence behind vaccines for melanoma, but he was not involved in the current research.
But for several reasons, he says, "It's not a home run."
For one thing, he says, there's no way for doctors to predict which patients might have a response to the vaccine treatment.
And the vaccine can't be used in everyone. The inoculation only works in people with a certain type of protein signature on the surface of their cells, called an HLA type, though researchers said the vaccine could be tailored, in the future, to work with different HLA types.
Patients also have to be healthy enough to withstand the toxic effects of treatment, which can be significant.
But for patients who are battling advanced melanoma, which is one of the deadliest kinds of cancer, any options, even limited ones, are likely to be welcome news.
"Cancer patients want to do something to fight their cancer, but if you have stage II or stage III disease, the standard of care is observation," says Tim Turnham, PhD, executive director of the Melanoma Research Foundation in Washington, D.C. "That's really tough for patients."
Using Vaccines to Fight Cancer
For the study, researchers recruited 185 patients at 21 centers across the U.S.
To be eligible for the study, patients had to have metastatic melanoma, either stage IV or locally advanced stage III, and they had to be HLA-type A0201, a tissue type carried by about half of people in the U.S.
All patients received high-dose IL-2 therapy. IL-2 was approved by the FDA in 1998 for the treatment of metastatic melanoma.
About half of patients, 91, were randomly assigned to also receive the experimental gp100 vaccine. That vaccine uses a protein found on the surface of cancer cells to flag those cells so they can be destroyed by the immune system.
Radiologists who weren't told which group was getting the vaccine reviewed scans to determine tumor progression.
Just 6% of patients who got IL-2 alone saw their tumors shrink by at least 50%. In the vaccine group, however, 16% saw that much improvement.
The midpoint for progression-free survival was 1.6 months in the IL-2 only group, compared to 2.2 months in the vaccine group.
The median for overall survival was 11.1 months in the group that only received IL-2 compared to 17.8 months in the vaccine group. This indicates a trend in increased in overall survival in the vaccine group.
"The numbers are small, if you look at the absolute numbers in terms of the benefit," says study researcher Douglas J. Schartzentruber, MD, a surgical oncologist who is medical director of the Indiana University Health Goshen Center for Cancer Care.
But he points out that the first drug ever to demonstrate a survival benefit for patients with melanoma, Yervoy, was just approved last month by the FDA.
"We're just beginning to develop some effective treatment strategies for metastatic melanoma and, in this case, the vaccine is proof of principle that vaccines have a role," he says.