Two snippets about colon cancer in the news recently:  one (EurekAlert) determines that obesity ( here a BMI of over 40) raises the risk of neoplasia by a factor of 5.2.  

The other, published in the Nov. 17 issue of the Journal of the National Cancer Institute, suggested that high levels of selenium in the blood translated into a 34% lower risk of colon cancer.

This is also supported by an older study from 1977, which showed selenium was protective against chemically induced cancers of the colon. 

Read my article about the importance of Selenium here.