What Is the Prostate Cancer Vaccine?
The prostate cancer vaccine Provenge can help extend the life of men with advanced stages of the disease that have exhausted primary treatment options. Unlike a typical vaccine given to prevent infection with a virus like influenza or polio, the prostate cancer vaccine treats the existing disease. The vaccine, sipuleucel-T, was approved by the American Food and Drug Administration (FDA) in April 2010. Although it does not cure prostate cancer, the vaccine appears to have mild side effects in comparison to other treatments like chemotherapy or medication.
Sipuleucel-T is made using the patient’s own white blood cells. The cells are removed and sent to a lab where they are exposed to a prostate cancer cell protein. Approximately three days later, the patient receives the cells in a process akin to a blood transfusion. The process is repeated three times with a two-week break between doses. The prostate cancer vaccine works by stimulating a patient’s own natural defenses to help fight cancer cells, cells that otherwise effectively evade detection by the immune system.
The FDA approved the prostate cancer vaccine sipuleucel-T based on the results of a randomized phase III study. A phase III study consists of multicenter trials on patient groups of between 1,000 to 3,000 people and is long and expensive. The goal of such a trial is to produce the definitive assessment of a drug’s effectiveness, monitor side effects, and compare it to standard treatment options.
The study demonstrated that men who received the vaccine lived on average four months longer than men who received a placebo injection. After three years, 32 percent of the men given the vaccine were alive, compared with 23 percent of those who received the placebo. In comparison, docetaxel, the current standard treatment for prostate cancer that does not respond to hormone therapy, typically adds around two months to a patient’s life.
Not all patients will benefit from the prostate cancer vaccine. The FDA has only approved sipuleucel-T for use against cancers that no longer respond to hormone therapy. Additionally, the series of three injections can be prohibitively expensive for a survivor benefit that is limited but genuine.
Chemotherapy is a primary treatment for prostate cancer but it can cause serious side effects like fatigue, weight loss and infections. The prostate cancer vaccine generally causes comparably mild symptoms. Most men who receive sipuleucel-T develop chills, headaches and fever. These side effects typically dissipate within a few days of the injection.
In addition to sipuleucel-T, a second prostate cancer vaccine called PROSTVAC-VF may eventually be approved. PROSTVAC-VF is a vaccine that uses a genetically-modified virus containing prostate-specific antigen (PSA). A patient’s immune system responds to the virus in the vaccine and will begin to destroy cancer cells that contain PSA. PROSTVAC-VF was in early-stage clinical trials in November 2010.
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