Selenium is an Antioxidant

Dr. Richard Donaldson of the St. Louis Veterans' Administration Hospital conducted a clinical trial with terminally ill cancer patients. He found that when he could raise the patients' blood levels of selenium into the normal range, their pain and tumor sizes were often reduced.In a 140 patient study of cancer victims treated with selenium, Dr. Donaldson reported in 1983 that some patients deemed terminal with only weeks to live were completely free of all signs of cancer after four years; all the patients showed a reduction in tumor size and in pain.[1]

Selenium, especially when used in conjunction with vitamin C, vitamin E and beta-carotene, works to block chemical reactions that create free radicals in the body (which can damage DNA and cause degenerative change in cells, leading to cancer).

[1] Richard A. Passwater, Cancer and Its Nutritional Therapies (New Canaan, CT: Keats Publishing, 1983), p. 149.