CHAPTER 25: The Selenium and Vitamin E Cancer Prevention Trial (SELECT): Prevention of Prostate Cancer Using Selenium and/or Vitamin E in the SELECT Cancer Prevention Trial

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was conducted to assess the efficacy of selenium and vitamin E alone and in combination on the incidence of prostate cancer. In this randomized, double-blind, placebo-controlled, 2 × 2 factorial design clinical trial, neither selenium nor vitamin E reduced the incidence of prostate cancer after seven years, and in fact, vitamin E was associated with a 17% increased risk of prostate cancer compared to placebo. The null findings were initially surprising given the preclinical and clinical evidence suggesting chemopreventive activity of selenium. These findings suggest that selenium and vitamin E do not prevent prostate cancer. Other potential explanations for the null findings include the agent formulation and dose, the characteristics of the cohort, and the study design. It is likely that only specific subpopulations may benefit from selenium supplementation; therefore, future studies should consider the baseline selenium status of the participants, age of the cohort, and genotype of specific selenoproteins, among other characteristics, in order to determine the activity of selenium in cancer prevention.