Vaccination may well be the most significant public health measure ever introduced.  By stimulating the immune system, vaccines protect us against a host of viral and bacterial diseases.  But now there’s hope that vaccines can do more than ward off diseases such as the measles, mumps, rubella or the flu; they may actually treat disease.

An invasion by bacteria or viruses can make us sick.  If we’re lucky, we get away with a few days of fever, maybe a touch of diarrhea.  If we’re unlucky, the symptoms can be far worse.  In any case, our body is not pleased with the onslaught and takes measures to prevent another such experience.  How?  By assembling special proteins called antibodies that can recognize and destroy the microbe in question on a subsequent exposure.  The idea behind a vaccine is to trick the body into generating antibodies to a microbe without causing disease.  This is done by injecting a weakened or dead form of the microbe that can’t cause disease but is still capable of stimulating an immune response.

So far, vaccines have been used as a prophylactic measure, meaning that they prevent, or at least dampen, future infections. But in April, 2010, the U.S. Food and Drug Administration (FDA) approved Dendreon’s “Provenge,” a vaccine designed to treat prostate cancer. This cancer usually strikes men over fifty, and is the most common type of male cancer in North America, with some 200,000 new cases in 2008 and 30,000 deaths. It is the second leading cause of cancer death in men after lung cancer, although many men with prostate cancer experience no symptoms, undergo no treatments, and eventually die of other causes.

Hormone therapy is a common treatment option for prostate cancer or benign prostate hyperplasia (enlarged prostate that may or may not develop into cancer). Finasteride, for example, is an antiandrogen, meaning that it blocks the action of male hormones, thereby reducing prostate size. Other treatments include surgery, radiation, chemotherapy, and high intensity focused ultrasound. Treating cancer with a vaccine, however, is a novel idea.

Simply put, Provenge is made by extracting cancer cells from a patient’s tumour and exposing these to white blood cells taken from the same patient. White blood cells are immune cells that attack foreign or non-self substances. A protein called PAP-GM-CSF fusion protein is then added to the mixture to enhance the vigour of the white blood cells’ attack on the cancer cells. The result is a vaccine that increases our immune function against a specific disease.

Unfortunately, this treatment is not intended for all patients with prostate cancer but only for men with so-called “metastatic castration-resistant” prostate cancer. For these individuals, the cancer has spread beyond the prostate and they no longer respond to hormone therapy. Studies have shown that Provenge prolongs survival by about four to four and a half months.  The price for those extra months is steep, in the neighbourhood of $50,000 to $100,000 for the three required dosages. One might wonder if delaying death by a mere four months is worth the expense, especially if there is not much joy to be had.

But that doesn’t mean Provenge is not a significant treatment.  It is.  In fact, it is a breakthrough of sorts.  Provenge is proof of concept that vaccination can serve as a treatment for cancer.  Today Provenge buys men stricken by severe prostate cancer four more months of life. Next year, it might be ten months. One day, it might be a decade.