Selenium (Se) is an essential and unique micronutrient for a number of biological processes; deficiency of dietary selenium is associated with an increased incidence of cancers in epidemiological and clinical trial.[1] Selenium exerts its anticarcinogenic effects mainly through selenoproteins at nutritional levels; 25 selenoproteins have been identified in the human genome at least.[2,3] Generally, selenoproteins can be classified into 3 categories.[4] First, there are selenoproteins that have incorporated Sec under a precise process requiring the UGA codon. The gene discussed is SELENOS; the disease is cancer.