The chances of having a normal colonoscopy 1 year ago and becoming advanced bowel cancer 1 year later are relatively low. The process of colorectal tumor formation is relatively slow, from colon polyps to cancer often takes 10 years. If colonoscopy was done 1 year ago and found intestinal polyps such as villous adenomas, or there is a history of chronic colitis for many years, cancer may appear 1 year later. However, if the colonoscopy was normal 1 year ago, most cancers will not form after 1 year. Some people who have normal colonoscopy 1 year ago and become cancerous 1 year later may have missed the diagnosis during colonoscopy 1 year ago, because the intestinal tube is long and peristaltic all the time, and there is a possibility of incomplete observation during colonoscopy. It is suggested that patients should consult the doctor in time after finding cancer to avoid delaying the condition.