Does having an adenomatus colonic polyp in one's late 20s indicate a significantly increased chance of colon cancer later in life?

Depends: On whether it is part of a genetic predisposition such as hereditary non-polyposis colon cancer (hnpcc), or an isolated event and you never have another polyp. Your GI doc will recommend the appropriate follow-up to minimize the risk of cancer.

Screening : 1. Family history would be very important. 2. If polyp, next one in 3 years. Once you get a completely clean one then perhaps every 5 years. The purpose of close surveillance is to detect polyps and precancerous lesions.