Colorectal cancer begins in the colon or the rectum. This type of cancer can be called either colon cancer or rectal cancer depending on where it starts, according to the American Cancer Society. These cancers both affect the digestive system.
A noncancerous polyp first develops on the inner lining of the colon or rectum. Although a polyp is noncancerous tissue, it can develop into cancer depending on the kind of polyp that it is, states the American Cancer Society. Adenomatous polyps can change into cancer, while hyperplastic polyps and inflammatory polyps are generally not precancerous. When a polyp becomes cancerous, the cancer starts growing into the wall of the rectum or colon and into blood or lymph vessels. More than 95 percent of colorectal cancers are adenocarcinomas, or cancers that affect cells responsible for lubricating the inside of the colon and rectum, adds the American Cancer Society.
Colon cancer is highly treatable if it is discovered early, notes the Colon Cancer Alliance. Treatments include surgery, chemotherapy and radiation. A person's risk of developing colorectal cancer increases after the age of 50, and it is important for everyone over the age of 50 to get screened, according to MedlinePlus. A colonoscopy can be used to test for blood in the stool, and surgery can cure colorectal cancer if it is detected early.