Combining Vaccine and Antiandrogen Therapy for Prostate Cancer
Name of the Trial
Vaccine Therapy with PROSTVAC/TRICOM and Flutamide versus Flutamide Alone to Treat Prostate Cancer (NCI-07-C-0107). See the protocol summary.
Dr. Ravi A. Madan, NCI Center for Cancer Research
Why This Trial Is Important
Men with prostate cancer who show signs of progressive disease, such as an increasing level of prostate-specific antigen (PSA) in their blood, after treatment with surgery or radiation therapy may undergo another type of treatment called androgen deprivation. Androgen deprivation involves either physical or chemical castration to block the production of testosterone, a male sex hormone that often drives prostate cancer growth. Despite this treatment, some men may continue to experience an increasing PSA level but show no evidence of metastatic disease on imaging scans. These patients are said to have castration-resistant, nonmetastatic prostate cancer (also called stage D0.5 disease). Currently, there is no standard of care for men with this stage of prostate cancer.
A recent study by NCI researchers indicated that combining a therapeutic prostate cancer vaccine that targets the PSA protein with an antiandrogen drug that blocks the binding of testosterone to the androgen receptors in cancer cells may help delay disease progression in these men. Antiandrogen drugs can supplement androgen deprivation therapy in preventing the remaining testosterone in the body from promoting prostate cancer cell growth.
In this clinical trial, men with castration-resistant, nonmetastatic prostate cancer who are undergoing androgen deprivation therapy will be randomly assigned to undergo antiandrogen treatment with the FDA-approved drug flutamide with or without the addition of a PSA-targeting vaccine called PROSTVAC/PSA-TRICOM. Men in the study will take flutamide pills three times a day and potentially receive the vaccine subcutaneously once a month until disease progression. Doctors will monitor the men for signs that the cancer is progressing.
“We hope to attack prostate cancer both hormonally using the androgen blockade of flutamide and immunologically with the vaccine. We believe the vaccine may be able to ‘wake up’ the immune system and have it attack and destroy prostate cancer cells,” said Dr. Madan. “There is some preclinical evidence that suggests that lowering testosterone and then introducing a vaccine may enhance an immune response.
“The vaccine itself does not cause significant side effects,” Dr. Madan added. “Flutamide has some side effects that patients undergoing testosterone-lowering therapy are familiar with, but the main side effects we see with the vaccine are irritation at the injection site and some men experience a mild fever that usually goes away on its own.”