Colorectal cancer, also known as colon cancer, is the development of cancer in the colon or rectum. This cancer can occur in any part of your lower digestive tract—the large intestine. The last several inches of the large intestine is referred to as the rectum. Cancer that occurs in the upper portion of the large intestine is called colon cancer, and the lower portion of the intestine, the rectum, is called colorectal cancer. Cancer is due to the abnormal growth of cells that have the ability to invade or spread to other parts of the body. In the colon, these growths start as noncancerous polyps. Over time, these polyps can become colon cancer. It usually takes up to 10 years or more for this change to occur.