In late October, the National Cancer Institute (NCI) decided to halt the Selenium and Vitamin E Cancer Prevention Trial (SELECT) because an initial, independent review of study data showed that selenium and vitamin E supplements, taken either alone or together, did not prevent prostate cancer. The study, funded by NCI and other institutes that comprise the National Institutes of Health (NIH), 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, as well as 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, NCI stressed that neither of these findings proves an increased risk from the supplements and both may be due to chance.

SELECT participants are currently receiving letters explaining the study review and telling them to stop taking their study supplements. 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. As follow-up of the SELECT participants continues, the participants will continue to be blinded. A blinded follow-up may avoid unintentional bias and potentially false conclusions. However, at the request of a participant, they will be informed which supplement, if any, they received.

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% fewer prostate cancers in men who took the supplement, and a 1996 study of 1312 men and women with skin cancer who took selenium for prevention of the disease showed that men who took the supplement had 52% 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 8000 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 was always designed as a study that would answer more than a single question about prostate cancer,” said Eric Klein, MD, 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.”