NCI pulls plug on study of supplements and effects on prostate cancer

BETHESDA, Md. The National Cancer Institute last week reported that selenium and vitamin E supplements, taken either alone or together, do not prevent prostate cancer, citing an independent review of study data from the Selenium and Vitamin E Cancer Prevention Trial that was funded by NCI and other institutes that comprise the National Institutes of Health.

The data also showed two concerning trends: a small but not statistically significant increase in the number of prostate cancer cases among the more than 35,000 men age 50 and older in the trial taking only vitamin E and a small, but not statistically significant increase in the number of cases of adult onset diabetes in men taking only selenium. Because this is an early analysis of the data from the study, neither of these findings proves an increased risk from the supplements and both may be due to chance, NCI noted.

As a result of the review, NCI is pulling the plug on the study. SELECT participants are receiving letters explaining the study review and telling them to stop taking their study supplements. However, participants will continue to have their health monitored by study staff, which may include regular digital rectal exams and PSA (prostate-specific antigen) tests to detect prostate cancer. Investigators intend to follow the participants for about three years to determine the long-term effects of having taken either supplement or placebo and to complete a biorepository of blood samples that will be used in extensive molecular analyses to give researchers a better understanding of prostate cancer, other cancers, and other diseases of male aging.

“SELECT was always designed as a study that would answer more than a single question about prostate cancer,” stated Eric Klein, a study co-chair for SELECT, and a physician at the Cleveland Clinic. “As we continue to monitor the health of these 35,000 men, this information may help us understand why two nutrients that showed strong initial evidence to be able to prevent prostate cancer did not do so.”

SELECT was undertaken to substantiate earlier, separate findings from studies in which prostate cancer was not the primary outcome: a 1998 study of 29,133 male smokers in Finland who took vitamin E to prevent lung cancer surprisingly showed 32 percent fewer prostate cancers in men who took the supplement, and a 1996 study of 1,312 men and women with skin cancer who took selenium for prevention of the disease showed that men who took the supplement had 52 percent fewer prostate cancers than men who did not take the supplement.

Based on these and other earlier findings, in 2001, men were recruited to participate in SELECT. They were randomly assigned to take one of four sets of supplements or placebos, with more than 8,000 men in each group. One group took both selenium and vitamin E; one took selenium and a vitamin E placebo; one took vitamin E and a selenium placebo; and the final group received placebos of both supplements.

SELECT has been funded by NCI for $114 million, with additional monies from the National Center for Complementary and Alternative Medicine, and with sub-studies funded and conducted by the National Heart, Lung and Blood Institute, the National Institute of Aging and the National Eye Institute at NIH. The sub-studies were evaluating the effects of selenium and vitamin E on chronic obstructive pulmonary disease, the development of Alzheimer’s disease, and the development of macular degeneration and cataracts, and will continue without participants taking study supplements. An NCI-funded substudy is looking at the effects of the supplements on men who developed colon polyps.