The United States Food and Drug Administration (FDA) recently approved Dendreon Corporation’s “cancer vaccine,” Provenge, for the treatment of certain types of prostate cancer. It became the first cancer vaccine to be approved for use in the United States. (Gardasil, Merck’s HPV vaccine, is sometimes referred to as an anti-cancer vaccine since it prevents infection with strains of HPV that cause cervical cancer. Dendreon’s product, however, is designed to directly treat cancer.)
Provenge is not a vaccine in the same way we would think about vaccines against measles, polio, or other infectious diseases. Those vaccines are designed to prevent infection by priming the immune system against a particular pathogen: a strain of a virus is weakened or inactivated, for example, and a mass-produced vaccine is created that can be administered for future protection against that virus before it can take hold in the body.
Provenge, however, is designed to treat existing cases of advanced prostate cancer, not prevent cancer. It works in a similar way to what we think of as a typical vaccine: by priming a person’s immune system to attack the disease. Attacking cancer is complicated, however, since cancer cells are actually the body’s own cells, making it difficult to “teach” a person’s immune system to identify them. Provenge is designed to stimulate a T-cell response to prostate cancer cells that are present.
There is yet another complication, however: since cancer cells are essentially just a person’s own cells gone haywire, they very from patient to patient. That means that no one vaccine can be mass-produced and administered to stimulate different immune systems to attack cancer cells–at least not yet. So instead, Provenge is created on an individual basis: some of the patient’s own immune cells are collected and used to generate the vaccine. The cells are processed with a recombinant protein that “acts” like an antigen associated with prostate cancer: it can provoke an immune response against the cancer cells when the resulting vaccine is introduced to the patient’s body.
The new vaccine has been demonstrated to extend the life of advanced prostate cancer patients by a median of about four months. Unfortunately it is quite expensive–Dendreon has announced that a total course of treatment with Provenge, consisting of three doses given about weeks apart, will cost about $93,000. In addition, its mechanism of treatment is not entirely understood. Prostate-Specific Antigen levels, for example, are often used to detect prostate cancer. PSA is a protein created by the prostate gland; increased levels of it in the blood can be an indication of prostate cancer. In trials, however, Provenge did not always lower PSA levels as one might expect during treatment, even when a patient’s survival time increased. So the treatment does extend survival times–researchers just aren’t sure how yet.
Still, it’s a promising step against a disease that kills more than 27,000 people in the United States each year. The treatment opens up many possibilities for future cancer vaccines and combined treatment options. In the meantime, Provenge will be made available to 2,000 prostate cancer patients in its first year of manufacture.
For more information about prostate cancer: National Cancer Institute
For information about Provenge from Dendreon Corporation: Provenge.com
To see the package insert for Provenge, detailing full prescribing information: U.S. Food and Drug Administration