One wonders when we will apply the knowledge that we already have. See:
Feng Y, Finley JW, Davis CD, Becker WK, Fretland AJ, Hein DW. Dietary Selenium Reduces the Formation of Aberrant Crypts in Rats Administered 3,2'-Dimethyl-4-aminobiphenyl. Toxicology and Applied Pharma 157:36-42, 1999.
Selenium is an essential trace element for human health and has received considerable attention for its possible role as an effective, naturally occurring, substance that has cancer preventive properties. Colon cancer is the second leading cause of cancer deaths in the United States and fourth most common cause of cancer deaths worldwide. Anatomical lesions leading to cancer have been detected in human colon resections and in experimental animals treated with chemicals that cause cancer. We observed that the frequency of these anatomical changes was significantly reduced in animals treated with a chemical causing cancer and supplemented with various selenium salts, selenate and selenite, but not when supplemented with selenomethionine, an amino acid containing selenium. These results suggest that selenite and selenate can be protective against chemically induced colon cancer.



Clark et al, Effects of Selenium Supplementation for Cancer Prevention in Patients With Carcinoma of the Skin . JAMA, December 25, 1996-Vol 276, No. 24
Intervention agent was 200 mmg of selenuim supplied as a 0.5-g high-selenium brewers yeast tablet [Nutrition 21, LaJolla, Calif.]