As a retired gastroenterologist I am still particularly interested in gastrointestinal illnesses. People often ask me about colorectal cancer, so I will begin this series by writing about this disease.

Colorectal cancer is the third most common type of cancer in the United States. There were almost 100,000 new cases reported last year.

Colorectal cancer is cancer that starts in the colon or rectum. The colon and the rectum are parts of the large intestine, which is the lower part of the body's digestive system. Colorectal cancer almost always begins as a growth called a polyp, an abnormal growth which may form on the inner wall of the colon or rectum. Some polyps become cancerous over time.

Doctors use a colonoscope to check the inside of the colon. A long, flexible tube with a camera on one end is inserted into the rectum and then advanced to the cecum, the first part of the colon. All suspicious growths can be biopsied for diagnostic purposes. If polyps are found, they can be removed. This procedure is a colonoscopy. Since the onset of the disease usually begins after age 50, screening for colorectal cancer should begin soon after you turn 50, then continue at regular intervals after that.  

The slow course of growth from precancerous polyp to invasive cancer provides an opportunity for the prevention and early detection of colorectal cancer. Screening can prevent cancer through the detection and removal of precancerous growths, as well as detect cancer at an early stage, when treatment is more successful. As a result, screening reduces colorectal cancer mortality both by decreasing the incidence of disease and by increasing the likelihood of survival.