Results from a Southwest Oncology Group (SWOG) study show that radiotherapy given to men with locally advanced prostate cancer after their prostate gland is removed does not significantly reduce the risk of subsequent cancer spread to distant sites but significantly lowers the risk of the cancer recurrence compared to men who do not receive radiation. The results were presented at a press conference in conjunction with the publication of the study results in the November 15, 2006, issue of the Journal of the American Medical Association.
The study involved 425 men enrolled from 1988 through 1997, but whose health was followed through September 2005 for the purpose of long-term analysis. All the men in the study had surgery to remove their prostate gland and were found to be at a higher risk of cancer recurrence based on the extent of their cancer. These men were then randomly selected to receive either radiation or observation only during the study. There were 214 men in the group who received radiation and 211 who did not. The primary goal of the study was to determine if radiation would prevent subsequent spread of cancer to other areas of the body, generally to lymph nodes and bone.
Study results found a reduction in spread of cancer with radiation, but the degree of reduction did not achieve statistical significance; radiation did reduce the risk of cancer coming back, reducing risk by about 40%. Additionally, men who had a low prostate-specific antigen (PSA) level after surgery and who received radiation had a significantly lower risk of subsequent development of a measurable PSA after surgerya sign of possible cancer recurrence.
"This is the second randomized study to evaluate the role of immediate postoperative radiation therapy on long-term results in the treatment of prostate cancer," said Gregory P. Swanson, MD, co-investigator on the investigation known as SWOG-8794. The intergroup trial involved 108 institutions across the United States and Canada.
"These study results in this group of men with prolonged follow-up, considered in combination with the results of a larger European study, show that radiation significantly reduces the risk of prostate cancer recurrence after surgery," said Swanson, associate professor of radiation oncology and urology at the University of Texas Health Science Center in San Antonio. "No other postoperative treatment has been shown to impact the risk of recurrence this dramatically. Patients who have a high risk of prostate cancer recurrence after surgery should be informed of these findings, especially before embarking on any other form of treatment, because no other treatment has been shown to have this degree of effectiveness."
While the study showed that radiation reduced the risk of prostate cancer coming back, there were a number of other important results. The study's primary goal was to find out whether radiation following removal of the prostate gland reduced a man's risk of developing cancer metastasis.
In fact, the study found that radiation reduced this risk by 25%, extending the time to metastasis from 13.2 to 14.7 years, but this difference was not sufficiently different to be considered statistically significant. In the radiation group, 35.5% of the 214 patients were diagnosed with metastatic prostate cancer or died from any cause compared to 43% of the 211 patients in the observation group. Although no statistically significant improvement in survival was achieved, there were 83 deaths in the radiation group, which had a median survival of 14.7 years, and 71 deaths in the observation-only group, with a median survival of 13.8 years.