Mutations in the adenomatous polyposis coli (APC) tumor suppressor gene have been found to cause 85 percent of colon cancers. Now researchers at the University of Utah’s Huntsman Cancer Institute know why. In a paper published on-line Sept. 9 in the Journal of Biological Chemistry, they explain that APC controls the conversion of dietary vitamin A into retinoic acid. If this process is impaired, colon cancer can result.