Introduction
Colon cancer screening comprises a variety of diagnostic tests to detect polyps and early cancers in the colon (large intestine). The large intestine, also known as the large bowel, is the last section of the gastrointestinal tract and the digestive system. It includes the colon, rectum, and anus. Colon cancer screening can detect abnormalities and address them before the cancer develops or spreads. Regular screenings may decrease the risk of death and complications caused by colorectal cancer.
Indications
Almost all colon cancers begin as benign or noncancerous polyps, some of which may slowly develop into cancer. Colon cancer screening can detect these polyps and early cancers.
Colon cancer is the uncontrolled division of abnormal cells in the large intestine. Cancer of the colon develops from one or more polyps, small and non-cancerous growths of tissue. The cancer usually begins in the glands lining the colon and rectum. The initial non-cancerous tumour gradually develops into cancer which spreads to nearby tissues, lymph nodes or distant organs (in the later stages), disrupting their function. Although colon cancer can affect people of all ages, it is more common in those 60 years and over. Certain factors that increase the risk of developing colon cancer include alcohol, smoking, high fat intake, a family history of colon cancer, the presence of polyps, and advanced age (>60 years).
Screening Tests
Colon or colorectal cancer can often be averted through regular screenings that can detect polyps before they become cancerous. In general, people with an average risk should start screening at age 45. There are several tests used to screen for colon cancer, including:
- Stool Tests: Polyps in the colon and smaller cancerous growths can cause small amounts of bleeding not visible to the naked eye. The most common test for detecting this hidden blood is the fecal occult blood test (FOBT) which looks for hidden (occult) blood in the stool. The test involves microscopic analysis of your stool in a laboratory. Two related tests are the stool DNA test (sDNA) and the faecal immunochemical test (FIT). The stool DNA test examines DNA from an individual’s stool sample to check for cancer. It uses DNA changes that occur in the polyp or cancer to determine if a colonoscopy should be performed. The faecal immunochemical test analyzes antibodies to detect blood in the stool.
- Sigmoidoscopy: A sigmoidoscopy is a diagnostic procedure to inspect the inner lining of your rectum and lower end of the large intestine (sigmoid colon) for abnormalities such as tumours or polyps using a device called a sigmoidoscope - a thin, flexible tube with a tiny camera and light source at one end. The procedure involves placing the tube into your anus and moving it slowly through your rectum and into the sigmoid colon. As the test only looks at the lower end of the large intestine, it may fail to detect cancers that are located higher in the large intestine.
- Colonoscopy: A colonoscopy is similar to a sigmoidoscopy, but the whole colon can be seen. A colonoscopy is performed under general anaesthesia. The colonoscope (a flexible tube with a small camera and lens attached at one end) is inserted into the rectum and gently moved up through the colon until it reaches the cecum (the junction of the small and large intestine). The colonoscope is then withdrawn very slowly as the camera displays images of the colon and rectum on a monitor. Polyps or growths can also be removed during the colonoscopy, to be sent later for analysis.
- Barium Enema: A barium enema is an X-ray exam that can detect changes or abnormalities in the large intestine. During a barium enema test, a technologist fills your colon with barium liquid through an enema, and a static X-ray or fluoroscopy (live X-ray imaging) is performed. The barium allows your doctor to see the inner surface of the colon and rectum to detect polyps or cancerous areas. A double-contrast barium enema employs two types of barium for more detailed images.
- Computed Tomography (CT or CAT) Colonography: CT colonography, sometimes referred to as virtual colonoscopy, is a screening technique in which a CT scan creates cross-sectional pictures of the abdominal organs, enabling your physician to identify changes or abnormalities in the colon and rectum. To help produce clear pictures, a catheter (small tube) is placed inside your rectum to fill your colon with air or carbon dioxide. CT colonography may be a more suitable option for individuals who cannot have a traditional colonoscopy due to the risk of anaesthesia.
- Capsule Endoscopy: Capsule endoscopy is a diagnostic procedure that involves swallowing a small, capsule-sized camera that captures video of the inside of your intestines as it passes through the gastrointestinal (GI) tract. This method is still under study and is not part of standard screening at this juncture.
Summary
Colon or colorectal cancer is currently the second-highest cause of cancer death in the United States. However, when diagnosed early, many cases of colon and rectal cancers can be treated effectively. The ideal way to reduce your risk of colon cancer is to have regular colon cancer screenings. For individuals at average risk, physicians normally recommend starting screenings (usually colonoscopies) at age 45 and continuing them until age 75, at which point the need for screenings is reassessed.
