Is there some kind of precursor to colon cancer?

Yes: We think most colon cancers evolve from benign polyps of the lining of the colon. I personally view it as a largely preventable disease, as these polyps are easily removed on colonoscopy before they become cancers. Trick is to get people to do colonoscopy.

Yes: The majority of colon cancers arise in colon polyps, which are among the most common specimens that we pathologists see. There are a variety of types, most with some propensity to turn cancerous. Especially, folks with lynch's hnpcc are prone to get colorectal cancer without polyps. Talk about colonoscopy with your physician -- saves lots of lives.

Screening: Dr friedlander's excellent answer points out the problems with current trends suggesting that screening is not important. It is! as dr friedlander says, polyp removal saves lives. Because polyps that are not overtly cancerous, our numbers fail to capture how many people are avoiding cancer. Get screened!