Colonoscopy is highly regarded, but it has risks. Patients need anesthesia for the invasive procedure. In rare cases, the colon may bleed or perforate during the colonoscopy procedure. As with many diseases, early detection of colon cancer may make a big difference to patients' survival. Colon cancer screening tests are recommended for everyone aged 50 and older; people at high risk for colorectal cancer may need to start screening earlier. Colorectal cancer is the No. 2 cause of cancer-related deaths in the U.S. for men and women combined, according to the American Cancer Society.