Selenium and skin cancer:
A multi-center, double-blind, randomized, placebo-controlled trial of 1,312 patients with a history of basal cell cancers (BCC) or squamous cell cancers (SCC) and a mean follow-up of 6.4 years showed that 200 mcg of selenium failed to decrease the development of skin cancer and may increase the risk of BCC (by 10%) and SCC (by 14%) compared to placebo. However, the results also indicated that with supplementation, total cancer incidence was decreased by 37%, total cancer mortality was decreased 50%, and prostate cancer incidence was decreased by approximately 50% compared to placebo. All of these effects were statistically significant. Although lung and colorectal cancer incidence were decreased by 30% and 54%, respectively, those effects were not statistically significant. (7)