Colorectal cancer: Tests that lead to early detection
Colorectal cancer is a cancer of the large portion of the bowel [colon] or rectum. These cancers are common and deadly; approximately one-third of people who develop it die, making it one of the leading cause of cancer death.
However, screening tests make it possible to detect existing cancers at an early, treatable stage, before there are any symptoms. Screening tests can also help to prevent the development of colorectal cancer by identifying and removing early growths called polyps.
Adults should ideally undergo screening beginning at the age of about 50 or earlier, depending upon a person’s risk of developing colorectal cancer. Several different tests are currently available, and new tests are being developed; all of these tests have advantages and disadvantages. The optimal screening test depends upon a person’s preferences and their risk of developing colon cancer.
Effectiveness of screening
Most colorectal cancers develop slowly over many years. They begin as small, benign tumours called adenomatous polyps. These polyps grow, develop precancerous changes, eventually become cancerous, and later spread and become incurable. This progression takes at least 10 years in most people.
Colon cancer screening tests work by detecting cancer while it is still curable. Regular screening for and removal of polyps can reduce a person’s risk of developing colorectal cancer by up to 90 percent. In addition, early detection of cancers that are already present in the colon increases the chances of successful treatment and decreases the chance of dying as a result of the cancer.
Who should be screened?
Several factors increase an individual’s risk of developing colorectal cancer. Having one or more of these factors will determine the age at which screening should begin, the frequency of screening, and the screening tests that are most appropriate.
Small increases in risk
Several characteristics increase the risk of colorectal cancer two to several fold. While each individual risk factor adds some risk, risk is substantially increased if several are present together.
Family history of colorectal cancer
Having colorectal cancer in a family member increases the risk of getting the cancer, especially if it is a first degree relative (a parent, brother or sister, or child), if several family members are affected, or if the cancers have occurred at an early age (eg, before age 55 years).
Prior colorectal cancer or polyps — People who have previously had colorectal cancer have an increased risk of developing a new colorectal cancer. People who have had adenomatous polyps before the age of 60 years are also at increased risk for developing colorectal cancer.
Increasing age — Although the average person has a 5 percent lifetime risk of developing colorectal cancer, 90 percent of these cancers occur in people older than 50 years of age.
Lifestyle factors — Several lifestyle factors increase the risk of colorectal cancer, including:
A diet high in fat and red meat and low in fibre
Obesity and a sedentary lifestyle
Cigarette smoking
Some conditions greatly increase the risk of colorectal cancer.
Familial adenomatous
polyposis — Familial adenomatous polyposis (FAP) is an uncommon inherited condition that increases a person’s risk of colorectal cancer. Nearly 100 percent of people with this condition will develop colorectal cancer during their lifetime, and most of these cancers occur before the age of 50 years. FAP causes hundreds of polyps to develop throughout the colon.
Inflammatory bowel disease — People with Crohn’s disease of the colon or ulcerative colitis have an increased risk of colorectal cancer. The amount of increased risk depends upon the amount of inflamed colon and the duration of disease; pancolitis (inflammation of the entire colon) and colitis of 10 years’ duration or longer are associated with the greatest risk for colorectal cancer. Risk is not increased in people with irritable bowel disease.
Screening:
Four tests are currently recommended for colorectal cancer screening: the fecal occult blood test, sigmoidoscopy, double contrast barium enema, and colonoscopy.
Fecal occult blood test — Colorectal cancers (and, more rarely, polyps) often bleed, releasing microscopic amounts of blood into the stool. The blood is frequently not visible to the naked eye, requiring specialized tests for detection. The fecal occult blood test can be used to detect blood in the stool.
Some simple dietary restrictions for two days prior to testing can reduce the chance of a false positive test. These include: Eliminate red meat and drugs that may irritate the stomach lining (such as aspirin and certain strong pain-killer drugs). Vitamin C can cause a false negative test and should be avoided.
Sigmoidoscopy — Sigmoidoscopy allows direct viewing of the lining of the rectum and the lower part of the colon . This area accounts for about one-half of the total area of the rectum and colon. Procedure — Sigmoidoscopy requires that the patient prepare by cleaning out the lower bowel. This usually involves consuming laxatives, and using an enema shortly before the examination. During the procedure, a thin, lighted tube is advanced into the rectum and the left side of the colon to check for polyps and cancer. Biopsies (small samples of tissue) can be removed during sigmoidoscopy. The procedure may cause mild cramping; most people do not need sedative drugs and are able to return to work or other activities the same day.
Fecal occult blood test and sigmoidoscopy — Combined screening with a fecal occult blood test and sigmoidoscopy is a common practice and may be more effective than screening with either test alone.
Colonoscopy — Colonoscopy allows a clinician to see the lining of the rectum and the entire colon. It requires that the patient prepare by cleaning out the entire colon and rectum. This usually involves consuming a liquid that causes diarrhoea temporarily. The patient is given a mild sedative drug before the procedure. During colonoscopy, a thin, lighted tube is used to directly view the lining of the rectum and the entire colon. Polyps and some cancers can be removed during this procedure.
Barium enema test — A barium enema test provides a detailed x-ray picture of the rectum and the entire colon. A more accurate version of the test, called double-contrast barium enema, is usually recommended. During a double contrast barium enema test, liquid barium is inserted into the rectum where it coats the inside of the colon. The barium is then drained out and the colon is filled with air. A thin layer of barium is left on the colon wall, which allows x-ray images to show a detailed view of the colon wall, including structural abnormalities such as polyps and cancers.
Preparation for a barium enema including cleaning the colon by drinking a saline laxative. Some people experience mild cramping during the procedure. Sedative drugs are usually not necessary and most people can return to work or other activities after the test is completed.
(The writer is a Consultant Physician)