Sign up now for TIME's WorldWatch email newsletter. 1 Cells that line the colon are very active, constantly dividing and creating buds, known as polyps.
Most polyps are small, benign growths that eventually stop growing.
But a tiny percentage of these polyps keep growing, sometimes for 10 years or more. Various genetic mutations can transform them into cancerous tumors. As these tumors grow larger, they gather more mutuations and begin to burrow deeper and deeper into the muscle wall that surrounds the colon. Once the cancer invades the blood and lymph systems, malignant cells can break off and spread to other organs, such as the liver, lungs and stomach. Exercise Joggers in particular have a low risk of colon cancer.