Novel Combined Therapy for Prostate Cancer Proves Significantly More Effective

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 5-year follow-up study examining prostate cancer patients at Methodist found that both prostate-specific antigen (PSA) values and biopsy data significantly proved the strength of the combined therapy. Improvement was seen in patients with all stages of prostate cancer, compared to the reported results of patients receiving standard radiation therapy at other institutions.

Largest Trial of Its Type

The data show as much as 20% improvement in disease control over historical controls, even with lower doses of radiation and with no added toxicity to the patient. A total of 33 low-risk (PSA < 10 ng/mL, Gleason score less than 7) and 33 intermediate- to high-risk (PSA > 10 ng/mL, Gleason score greater than 7) patients were examined. Low-risk patients had 100% disease-free survival at 5 years, and the intermediate- to high-risk group had 90% disease-free survival at 5 years.

This finding could affect 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," Dr. Butler 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."

Viral 'Cargo Ship'

In the study, the common cold virus was used as a "cargo ship" to carry the herpesvirus gene. This gene agent, known as AdV-tk, was injected into the cancer cells of the prostate. Patients were also given oral valacyclovir (Valtrex), which is the same medication used against herpesvirus. 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 immunologic system to look for antigens on the outside of the cell that identify them as cancerous or noncancerous. This signal attracts dendritic cells or antigen-presenting cells that jump start the immunologic 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," Dr. Butler said. "The hope is to give patients permanent freedom from the disease."

Additional Benefit

Another major benefit to using gene therapy in addition to radiation is that it may eliminate the need for physicians to use hormonal therapy, which is commonly used to lower androgen levels in prostate cancer patients.

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

"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 Dr. Butler. "It may have the greatest benefit in the patients who have microscopic disease that has spread to other parts of the body that we cannot detect by our current imaging techniques."