Study finds radiation therapy for prostate cancer nearly doubles risk for rectal cancer

03/30/05

A University of Minnesota Cancer Center study indicates that men who undergo radiation therapy for prostate cancer have nearly double the risk of developing rectal cancer when compared to men who opt to have surgery to treat prostate cancer.

The study found that men who receive radiation for prostate cancer have about 70 percent higher risk of developing rectal cancer than those who underwent surgery, a risk similar to that posed by having a family history of the disease. This is the first study to quantify rectal cancer risk associated with prostate radiation. The entire study will be published April 1, 2005 in the American Gastroenterological Association (AGA) journal Gastroenterology.

Nancy Baxter, M.D., Ph.D., colon and rectal surgeon and researcher at the University of Minnesota's Medical School and Cancer Center, led the research team that conducted the study.

"While the findings of our study do not suggest that prostate cancer treatment should change, we recommend that the potential for developing rectal cancer be included in conversations between doctors and patients when considering the individualized course of treatment and surveillance for patients with prostate cancer," said Baxter.

"Additionally, we recommend that men who have had prostate radiation should be monitored for rectal cancer starting five years after treatment." She further advises that men undergoing radiation therapy for prostate cancer ask their doctor about the approved screening methods, regardless of their age.

Researchers used data from the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Registry to evaluate the effect of radiation on development of cancer in the rectum. More than 85,000 men, age 18 to 80, were included in this retrospective, population-based study. These men were diagnosed with prostate cancer from Jan. 1, 1973 to Dec. 31, 1994. A total of 30,552 men received radiation, of which 1,437 developed rectal cancer.

Prostate cancer is the most commonly diagnosed cancer in the United States – this year more than 230,000 men will be told they have prostate cancer; about 4,300 of them will be Minnesotans.

Radiation therapy for prostate cancer has been associated with an increased rate of pelvic malignancies, particularly bladder cancer. Findings of this study suggest that direct radiation to the rectum increases the risk of developing rectal cancer, but does not affect the risk of cancer in other parts of the colon.

Since the study results are based on men who were treated for prostate cancer before 1995, the risk of developing cancer may be reduced by the evolution of radiation delivery techniques. However, researchers say that even with today's technology, some portions of the rectum still receive a high dose of radiation. Therefore, the risk of rectal cancer may still exist and thus, until proven otherwise, men treated with radiation for prostate cancer need monitoring for rectal cancer beginning five years after treatment.

This research study was funded by a University of Minnesota Academic Health Center Seed Grant. In addition to Baxter, the research team included Joel Tepper, Department of Radiation Oncology and UNC/Lineberger Comprehensive Cancer Center at the University of North Carolina School of Medicine in Chapel Hill; and David Rothenberger, Beth Virnig and Sara Durham, all with the University of Minnesota.

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