Novel Combined Therapy for Prostate Cancer Proves Significantly More Effective

Newswise — A combination of radiation and suicide gene therapy is eliminating the spread of prostate cancer and providing a long term vaccine against the disease, according to a study presented at the American Society of Clinical Oncology's annual prostate cancer meeting in San Francisco recently.

Dr. Brian Butler, chief of radiation oncology at The Methodist Hospital in Houston, said the five-year follow up study examining prostate cancer patients at Methodist found that both PSA values and biopsy data "significantly" proved the strength of the combined therapy. There was improvement in patients with all stages of prostate cancer when compared to the reported results of patients receiving standard radiation at other institutions.

The data show as much as 20 percent improvement in disease control over historical controls, even with lower doses of radiation and with no added toxicity to the patient. Thirty-three low-risk (PSA less than 10, Gleason score less than seven) and 33 intermediate- to high-risk (PSA greater than 10, Gleason score greater than seven) patients were examined. Low-risk patients had 100 percent disease-free survival at five years, and the intermediate- to high-risk group had 90 percent disease-free survival at five years.

This finding could impact the more than 70,000 patients nationwide who experience a recurrence of prostate cancer each year. The study was the first in the United States to look at the combined benefits of both therapies, and remains the largest trial of its type anywhere in the United States.

"This method not only treats the tumor area with radiation," he said, "but it also creates a system of assassins to go out and look for these cancer cells throughout the body. We are using the body's own immunological system to help identify the cancer and kill it."

In the study, the common cold virus was used as a "cargo ship" to carry the herpes virus gene. This gene agent, known as AdV-tk, was then was injected into the cancer cells of the prostate. Patients are also given the drug Valtrex orally, which is the same medication used against the herpes virus. When the drug works to kill the herpes, it causes the cancer cells to self-destruct.

Gene agents also send out an inflammatory response, which signals the immunological system to look for antigens on the outside of the cell that identify them as cancerous or non-cancerous. This signal attracts specialized cells called dendritic cells or antigen presenting cells that jump start the immunological response against the cancer.

"This process allows the body to eliminate the spread of cancer by both being able to recognize cancer cells and sending out a constant barrage to kill it, just like a chickenpox vaccine does," he said. "The hope is to give patients permanent freedom from the disease."

In addition to prostate, this strategy of combining gene agents and radiation will be applied to multiple cancer sites in the near future, including lung, pancreas, rectal, anal, brain and renal cell.

"The possibility of using the patient's own cancer cells against the cancer in the form of a vaccine opens up a new arsenal of weapons for the radiation oncologist," said Butler. "It may have the greatest benefit in the patients that have microscopic disease that has spread to other parts of the body that we cannot detect by our current imaging techniques."

Another major benefit to using gene therapy in addition to radiation is that it may eliminate the need for physicians to use hormone therapy, which is common in treating prostate cancer. The purpose of hormone therapy is to lower the level of the male hormones, called androgens, which are produced mostly in the testicles. This is because androgens, such as testosterone, help the prostate tumor grow. Monthly shots can be given or the testicles can be surgically removed. Hormones often trigger negative side effects, such as hot flashes, decreased libido, anxiety and depression.