Combination Radiation/Vaccine Therapy for Prostate Cancer May Benefit Some Patients from National Institutes of Health News, US Dept of Health and Human Services.  May 2005

A pilot study of an experimental therapy for prostate cancer has found that a cancer vaccine can be safely administered to patients undergoing radiation therapy. In some patients receiving the vaccine, an immune response against tumor cells may occur, according to the results of a phase II clinical trial led by scientists at the National Cancer Institute (NCI), part of the National Institutes of Health. A strong immune response is an indication that the body is fighting the cancer.

This was the first trial to combine radiation and a cancer vaccine for treating prostate cancer, and the results now pave the way for a larger trial to evaluate the efficacy of the combination therapy in treating the disease. The combination therapy was well tolerated.

Cancer vaccines are intended either to treat existing cancers or to prevent the development of cancer. The experimental vaccine used in this study was designed to strengthen the body's natural defenses against prostate cancer.

"The idea is that you can stimulate the body's immune system to recognize and attack tumor cells through the use of a vaccine," explained James L. Gulley, M.D., Ph.D., of NCI's Laboratory of Tumor Immunology and Biology and the first author on the study. The study appears in the May 2005 issue of Clinical Cancer Research.

Thirteen of 17 patients who received the combination therapy had at least a three-fold increase in immune cells that attack a protein on the surface of tumor cells, compared to no detectable increases in eight patients who received radiation alone. The researchers also found evidence that the vaccine may have "revved up" the immune systems of some patients against other tumor proteins.

The rationale for testing a vaccine/radiation combination came from the preclinical observations that radiation can alter tumor cells in a way that makes it easier for the body's immune system to kill tumors. Furthermore, mice were cured of tumors when given local radiation plus vaccine, as compared with either treatment alone, which had minimal effects.

In addition, cancer patients who get hormonal therapy plus radiation tend to do better than those who receive radiation alone. The researchers hypothesized that stimulating the immune system with a vaccine might be another way to generate a "systemic" therapy that might work in conjunction with localized radiation.

An estimated 30 percent to 40 percent of patients treated with surgery or radiation for localized prostate cancer relapse within a decade.

"We have shown that this therapy is safe and well-tolerated — the first step toward finding alternative treatments for patients with localized prostate cancer, especially those at high risk for failing current treatments," said Gulley.