Some of the major signs of colon cancer are changes in bowel habits. That is, if you normally have a regular formed stool once a day, and suddenly you start having mucosy or bloody stools, even if it's just intermittently, this is not a normal bowel movement habit for you. This should be checked out because no one should have blood in their stool, and/or excessive amounts of mucous. When you go to your doctor and they do a screening test for colon cancer, they are actually checking for minute particles of blood in your stool, by doing a hemoccult test, which is a test to which they collect a small specimen of stool and put it on a special card, that then gets saturated in a test fluid, and turns blue if there's a presence of blood and/or high concentrations of iron. So, if you're getting tested for colon cancer by this hemoccult method, you should let your doctor know if you're taking any iron to treat anemia, because this can alter the result of your test.