Selenium (Se) is an essential trace element that is composed a variety of important enzymes. The relationship between low-serum Se levels to a higher cancer risk has attracted considerable attention in the area of cancer prevention (Fernandes et al. 2015). Adverse or beneficial health effects of Se are strongly dependent on the Se species (Marschall et al. 2016). However, how these Se compounds potentially exhibit anti-cancer properties are not fully understood.