The first therapeutic cancer vaccine

Time for some good news. This past week, the FDA approved the first-ever vaccine to treat cancer. The treatment is called Provenge, developed by a small company named Dendreon , and it’s designed for advanced prostate cancer. The idea of developing a vaccine to treat cancer has been around for a long time, but never before has a treatment made it all the way to the clinic. This is very good news, especially if it heralds many more new vaccine-like cancer treatments.

So what is Provenge? Unlike most vaccines, it’s not a simple shot. A typical vaccine contains some form of the infectious agent, usually a virus or a bacterium, which we administer as a shot (or a jab, as our friends in the UK put it). The virus is usually either dead or modified so that it cannot cause disease, but enough of it remains to “train” your immune system. The immune system reacts to the dead virus and, though the amazing mechanism of acquired immunity, is then primed to attack and eliminate a live virus (or bacterium) if it ever shows up again.

A cancer vaccine is not nearly so simple. Unfortunately, we can't just grind up a bit of cancerous tissue, treat it somehow, and then inject it. The reason this new treatment is called a vaccine is that, like conventional vaccines, it trains a person’s immune system to recognize and attack the unwanted invaders – in this case, the cancerous cells. But this presents a big problem, because cancer cells are the body’s own cells. How do we get the immune system to attack them without triggering a much broader, possibly damaging, autoimmune response? As Bruce Goldman explained in a 2002 article, the trick is to find some feature on the surface of cancer cells that marks them as abnormal, and then to get the immune system to target that feature (or antigen).

Luckily, because cancer cells have gone haywire, they tend to have lots of abnormal surface features. But every cancer tends to be a little bit different, which means that these antigens are different in each patient. That means that the vaccine has to be customized for each patient, an exquisitely difficult process. Cancer vaccines use another cell type, called dendritic cells, to create a vaccine that is customized for each patient: first a bit of the patient’s tumor has be collected, and then grown with dendritic cells, and then re-injected, which alerts the immune system to attack just the tumor cells. This is the process used in Provenge.

(Note that Provenge is the first therapeutic vaccine because it is used to treat cancer. There is already a preventive cancer vaccine available: Gardasil, which prevents some types of cervical cancer. But that’s another topic.)

Three years ago, the FDA rejected Dendreon’s first application, asking for more evidence that it worked. The company then conducted a new placebo-controlled, double-blind trial and found that Provenge (sipuleucel-T) extended patients' median survival time by 4.1 months. That might not sound like much, but for men with advanced prostate cancer, it’s better than anything else available. And this is only the additional survival time. Five years ago, Dendreon reported on an earlier study in which “34 percent of patients receiving Provenge were alive at 36 months compared to 11 percent of patients receiving placebo.” In that earlier study, median survival time increased by 4.5 months, essentially the same result as the newer study.

One disappointing part of the recent news is the price: Dendreon announced that it will charge $93,000 per patient. That’s an awful lot of money, and it’s not clear yet if insurance will cover this. No doubt desperate patients will be glad to pay for the few extra months of life. In fact, Dendreon said that its price is based on the assumption that people will pay $23,000 per extra month of life, based on the cost of other cancer drugs. We can only hope the price will drop dramatically as the company improves its manufacturing process, but (unfortunately) lower production costs don’t always get passed on to patients.

These are not miraculous results: Provenge is not a cure. And unlike conventional vaccines, it doesn’t prevent the disease; instead, it treats people who are already sick. But it’s a different type of treatment, and we can be optimistic that this opens the door for many improvements in cancer vaccines, not just for prostate cancer but for many other types of cancer. Trials are already under way for several other types of cancer, and the future looks very encouraging.