According to Philip M. Arlen, M.D., director of the Clinical Research Group for the Laboratory of Tumor Immunology and Biology, Center for Cancer Research, at the National Cancer Institute, “Vaccines, if and when they are approved, can be safely and effectively combined with other therapies, including hormones. There appears to be an advantage in overall survival.”
In realty, based on his study the use of cancer vaccines along with other traditional prostate cancer treatment holds out even greater potential for future prostate cancer treatment.
Arlen performed a study (phase II) that enrolled 42 patients who had castration-resistant prostate cancer. Randomly, these men were assigned to receive either a poxvirus-based prostate-specific antigen vaccine or hormone therapy with nilutamide. Once the prostate cancer showed signs of progression, patients were offered the other therapy as well as continuing to receive their original therapy.
A three-year survival probability for all the men enrolled in the study was 71 percent and the median overall survival was 4.4 years. The men who were randomized to the vaccine protocol had a three-year survival probability of 81 percent and an overall survival of 5.1 years, while the men taking only nilutamide had a three-year survival probability of 62 percent and an overall survival of 3.4 years. This is a statistically significant difference.
Of the 42 men who participated in the study, 12 men who were originally assigned to vaccine converted to nilutamide plus vaccine and eight men who were originally assigned to just nilutamide switched to vaccine plus hormone. The reason for the protocol switch was increasing levels of prostate-specific antigen (PSA), but without any evidence of metastasis.
For the men who received vaccine and then nilutamide, the three-year survival probability was 100 percent with a median overall survival of 6.2 years. For the men who switched to the vaccine after hormone therapy, the three-year survival probability was 75 percent with a median overall survival of 3.7 years.
These results are rather dramatic and need to be immediately followed up with a phase III study.
Arlen explained that the hormone therapy in combination with the vaccine works in two ways. “By using hormone therapy in prostate cancer you can help enhance your T-cell response to where the cancer is in the prostate gland, and you are also more likely to achieve a better immune response.”
Many of us are hopeful that the current pace of prostate cancer vaccine research will bring about an early approval from the FDA for a prostate cancer vaccine. A prostate cancer vaccine is not the same as the “normal” vaccine that is currently used for such problems as the flu or polio. These traditional vaccines help to develop an immune response before you are infected, thus allowing your body to fight off the ailment as you are exposed. Cancer vaccines are being designed to be administered after the cancer has been diagnosed. The vaccines would teach the immune system to recognize cancerous cells as foreign bodies and them eliminate them from the body.
Cancer vaccines are one of the most promising potential treatments that are being actively developed to fight all cancers, including prostate cancer. They continue to demonstrate great promise and could become available in the very near future (search Provenge in this blog).
Joel T Nowak, MA, MSW