Trial changes thinking on vitamin E supplements and prostate cancer risk
issue 14 | winter 2012
The largest prostate cancer prevention trial ever undertaken, the Selenium and Vitamin E Cancer Prevention Trial (SELECT), was built on the hypothesis that these supplements could lower a man's risk of developing prostate cancer. Now, researchers have concluded that vitamin E supplementation actually raised prostate cancer risk for men in the trial.
The finding comes 10 years after the study's launch by the SWOG clinical trials network based at the University of Michigan Comprehensive Cancer Center. SWOG (formerly the Southwest Oncology Group) is one of the largest cancer clinical trials cooperative groups in the United States.
SELECT enrolled more than 35,000 healthy older men, who were randomly assigned to take daily supplements of vitamin E, selenium, both or placebos.
The study closed early, in 2008, after interim data showed no preventive benefit on any arm. The early data also showed a slight increase in prostate cancer risk among the men who had taken only vitamin E, but the rise was not statistically significant at the time.
Three years of additional data have made that rise in risk even more pronounced and statistically significant. Over a seven-year period, there were 76 prostate cancer diagnoses per 1,000 men on the vitamin E-only arm, compared to 65 diagnoses per 1,000 men on the placebo arm. This represents a 17 percent increase in prostate cancers among men who took 400 International Units of vitamin E daily.
The findings appeared in the Journal of the American Medical Association.
The mechanism driving this increased risk remains a mystery, but researchers are hoping clues can be found among the almost 100,000 samples of blood, toenail clippings and tumors stored from the trial.
"SWOG is soliciting proposals from researchers nationwide to use the SELECT biorepository to help answer the biological question of why vitamin E increased risk instead of decreasing it," said Laurence Baker, D.O., professor of medicine and pharmacology at the U-M Medical School, study co-author and chair of SWOG.
Funding for the trial came primarily from the National Cancer Institute.