Colon cancer is the third leading cause of cancer-related death in the United States. The number of these deaths has significantly decreased due to screening colonoscopies. A colonoscopy is a procedure in which a physician examines the rectum and large intestines for abnormalities through the use of a specialized camera called an endoscope. Colonoscopies decrease the mortality associated with colon cancer through two main ways: by detecting and removing pre-cancerous lesions called polyps; and by detecting colon cancer at earlier stage, when therapies can still be effective at treating or removing the cancer.