The recently completed Selenium and Vitamin E Cancer Prevention Trial (SELECT) 
was one of the largest human cancer prevention trials ever undertaken. Its 
purpose was to assess the role of selenium and vitamin E in prostate cancer 
prevention, but SELECT found no decline in prostate cancer. Comparison of this 
study to other clinical trials involving selenium and to the results of animal 
studies suggests that the source of the selenium supplement, L-selenomethionine, 
and the relatively high initial levels of selenium in the enrolled men may have 
contributed to this outcome. Further analysis of the clinical and animal data 
highlights the need for mechanistic studies to better understand selenium 
biology in order to target dietary selenium to appropriate subsets of the human 
population: those individuals most likely to benefit from this micronutrient.