What is colon cancer?
Colon cancer is the uncontrolled growth of abnormal cells within the layers of tissue that line the colon. The colon is part of the digestive tract that processes nutrients, such as vitamins, minerals, carbohydrates and fat from food. It is five feet long and makes up the majority of the large intestine, also called the large bowel. In the path that food takes through the body (alimentary canal), the colon follows the small intestine and comes before the rectum. The colon absorbs water and salts, forms stools, and rids the body of waste.
Colon and rectum cancers are sometimes referred to together as "colorectal cancer." In this article, they will be referred to as "colon cancer." Together, they are the third most common non-skin cancer in adults and the second leading cause of cancer deaths in men and women in the United States after lung cancer.
Glands in the colon produce mucus and lubricate the lining of the colon and rectum. Most colon cancers are adenocarcinomas; they start in the cells that form these glands. Most cases of colon cancer begin with the development of benign polyps, finger-like growths that protrude into the intestinal cavity. These polyps are relatively common in people over age 50 and most remain benign. Some, however, can become cancerous with the ability to invade colon tissues and to spread to other parts of the body (metastasize). The tumors they form can create blockages in the intestine, preventing elimination.
The American Cancer Society (ACS) estimates the number of new colon cancer cases in the U.S. to be nearly 133,000 annually. The lifetime risk of developing colon cancer is about 1 in 20 (or 5%), according to the ACS. Within the last 20 years, however, the rate of colon cancer has dropped significantly. This is likely due to a few different factors. Improved screening has led to removal of more pre-cancerous polyps, preventing the development of cancer. Likewise, better screening has detected more cancers in the earlier stages, when they are most treatable; this has led to a decline in colon cancer deaths as well.