What is colon cancer and how does it start inside the body? Colon cancer begins in the large intestine and usually develops slowly over time. In many cases, it starts as small growths called polyps that form on the inner lining of the colon. These polyps are not always harmful at first, but some may turn into cancer if not treated early. Understanding what is colon cancer helps people become more aware of their digestive health. Early stages often show no clear symptoms, which makes awareness even more important. Factors like unhealthy diet, lack of physical activity, and genetic changes may increase risk. By learning about early causes and simple lifestyle changes, you can take better care of your colon health and reduce potential risks in the future.