The results are as predicted: the prostate cancer vaccine Provenge (sipuleucel-T) prolonged survival in men with hormone –resistant prostate cancer, but didn’t do anything to delay progression of the disease.
The results of a clinical trial studying this controversial vaccine were released this afternoon at the annual meeting of the American Urological Association in Chicago, and the news wires are already humming with the news.
Unfortunately, I still don’t have access to the actual abstract and have to rely on a news release from the company that ran the trial, which is not always the most satisfactory way for me to get information. Once I receive the abstract, I may update my comments if there is any significant new information.
According to the press release, 512 men participated in the trial. They were men who had prostate cancer that had progressed and was no longer responding to hormonal manipulation or medications. They were asymptomatic, which does put them in a better risk profile for long term survival, but this was true both for the men who received the vaccine and received a placebo. The study measured the overall survival of the participants.
For the men receiving Provenge, their survival was increased by 4.1 months compared to those who received the placebo (25.8 months vs. 21.7 months). 31.7% of the men receiving Provenge were alive at 3 years, compared to 23.0% of the men who received placebo. Side effects were reported to be very modest.
All of these results were statistically significant, which suggests that the results were not due to chance.
Unfortunately—and to me this is the unusual part of the trial--the vaccine did nothing to delay the progression of the disease. Vaccine or no vaccine, the time to progression was the same. Despite no delay in progression of the disease, survival was prolonged.
As mentioned in my previous blog, based on my interpretation of comments made in a prior conference call, these results are in line with past studies of this vaccine.
So what are the implications?
The treatment of advanced prostate cancer hasn’t made much progress in the past many years. There are some chemotherapy drugs that help, but they have significant side effects and don’t do much to improve survival. There aren’t many other alternatives out there—such as targeted therapy—that have received much notice for effectiveness in treating this very difficult-to-treat disease.
But we also have to remember that for several cancers the progress in treating the disease over the past 30 or 40 years hasn’t come in one big jump, but rather is the incremental advance of a couple of months here with one drug, and with another couple of months there with another drug.
As I mentioned in my prior blog, this report also advances a theory that has haunted many researchers and clinical investigators for years, namely how to create a vaccine from tumor cells that can harness the body’s own immune mechanisms that fight off viruses and bacteria (and probably small numbers of cancer cells that must exist in our bodies) to attack a cancer that has escaped from our own internal surveillance system.
Provenge has now broken through that barrier, and suggests that we may in fact be able to stimulate our body’s own defense mechanisms to aid our fight against cancer. This in itself is a truly remarkable accomplishment.
In the midst of this promise, I would be less than honest if I didn’t say that there are still some potential pitfalls.
First, as I mentioned a couple of weeks ago, this is a “top line” analysis of the results. A more detailed analysis and publication of the results—not to mention review by the FDA—still must be done.
There has been some background “noise” suggesting that there may be something about the way the men on the placebo arm were treated that may have influenced their survival adversely. Although this is unlikely—and difficult to prove—there is some chatter to that effect. That’s why the review of the data is so important.
The support for that concern can be found in the fact that the vaccine did nothing to delay progression of the disease. Usually, the situation is the other way around: the new drug delays progression of the disease, but may not increase survival. The normal way we think suggests that delay of progression is necessary before you see a survival benefit. That did not happen with Provenge. So, did the men who receive the placebo have something happen to them that may have shortened their lives compared to those who received Provenge? It isn’t likely, but it is possible.
That also leaves open to question whether or not the quality of life of the men who had their lives extended was also improved by the vaccine. Sometimes clinical trials measure quality of life (such as appetite, weight loss/gain, bone pain, ability to function, among others), sometimes they don’t. I don’t know whether or not quality of life was looked at in this trial. But it isn’t much of a life that is extended in intense pain, poor appetite, and wasting away.
All of these thoughts are speculation on my part, but offered in an effort to look beyond the headlines into the questions that will be asked by others as the data is reviewed.
The sooner we can see all of the data from the study, the sooner we can move forward with getting this drug to men who need it if it indeed meets the expectations that have been set with the release of today’s results.
That would be true progress.