COLON CANCER SCREENING
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Colorectal or colon cancer will occur in 5% of Canadians during their lifetime. After lung cancer, colon cancer is the number two killer of all cancers. Historically, women’s groups have promoted breast cancer awareness and men’s groups have taken up prostate cancer as their cause. Colon cancer has fallen ‘between the cracks’, so to speak. Public awareness for colon cancer has been slowly improving as governments have realized the significant cost of colon cancer to society.
Colon cancer is a cancer that develops in the large intestine (also known as the colon) or rectum. The primary goal of colon cancer screening is to prevent deaths from colon cancer. Screening tests can help identify cancers at an early and potentially treatable stage. Some tests can also prevent the development of colorectal cancer by identifying precancerous abnormal growths called polyps, which can be removed before they become malignant.
All adults should undergo colon cancer screening beginning at age 50 or earlier, depending upon their risk of developing colorectal cancer. Several tests are currently available, each of which has advantages and disadvantages. The optimal screening test depends upon your preferences and your risk of developing colon cancer.
EFFECTIVENESS OF COLON CANCER SCREENING
To understand how colonoscopy decreases deaths from colon cancer it is important to understand the relationship between colon polyps and colon cancer.
Finding polyps is important for colon cancer prevention, as small precancerous polyps grow into large polyps that then degenerate into cancer. This sequence of events is believed to take place over a period of at least 7–10 years. If someone has colon cancer, it started as a polyp first.
Colon cancer screening tests are effective by detecting polyps (the step before cancer) or by finding early stage cancers. When the polyp is removed during a colonoscopy you no longer have to worry about that polyp growing and turning into cancer. If an early-stage cancer is detected, surgery and other treatment options are more likely to be successful.
Regular screening for and removal of polyps reduces your risk of developing colorectal cancer by up to 90% with colonoscopy, and from 15–30% with fecal occult blood test (FOBT).
What follows is a review of colon cancer risks, available screening tests, and recommendations for screening based upon your risks. Related subjects: What is a Colonoscopy, Bowel Preparations, Crohn’s Disease and Ulcerative Colitis. (Charlie – please embed links)
COLON CANCER RISK FACTORS
Increase the Risk
While each individual factor contributes, risk is substantially increased if several are present together.
Family History – Risk of colorectal cancer increases if a family member who is a first-degree relative (a parent, brother or sister, or child) has had it, if he/she had polyps at a young age (under 60), if several family members are affected or if the cancers have occurred at an early age.
Personal History of Colon Cancer – People who have previously had colorectal cancer have an increased risk of developing a new colorectal cancer. People who have had precancerous polyps are also at increased risk for developing colorectal cancer.
Increasing Age – Although the average person has a 5% life-time risk of developing colorectal cancer, 90% of these cancers occur in people older than 50. Risk increases with age throughout life.
Lifestyle Factors – Several lifestyle factors increase the risk of colorectal cancer, including a diet high in fat and red meat and low in fiber, a sedentary lifestyle and cigarette smoking.
Familial Adenomatous Polyposis (FAP): an uncommon inherited condition that increases the risk of colorectal cancer. Nearly 100% of people with this condition will develop colorectal cancer during their lifetime, and most of these cancers occur before the age of 50. FAP causes hundreds of polyps to develop throughout the colon.
Hereditary Non-Polyposis Colon Cancer (HNPCC, also called Lynch Syndrome): another inherited condition associated with an increased risk of colorectal cancer. It is slightly more common than FAP, accounting for approximately 1-in-20 cases of colorectal cancer. About 70% of people with HNPCC will experience colorectal cancer by age 65. Cancer also tends to occur at younger ages. People with HNPCC are also at risk for other types of cancer, including cancer of the uterus, stomach, bladder, kidney, and ovary.
Inflammatory Bowel Disease –: individuals 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. The risk of colon cancer is not increased in people with irritable bowel disease.
Decrease the Risk
Although a few studies have shown that people who have higher calcium intake also have a lower risk of colorectal cancer, it is not known if taking calcium supplements or eating a high-calcium diet lowers the cancer risk. Aspirin, ibuprofen and related nonsteroidal anti-inflammatory drugs (NSAIDs) may decrease the risk of developing colorectal cancer; however, there is not enough evidence to recommend NSAIDs as a preventive treatment for colon cancer.
COLON CANCER SCREENING TESTS
Several tests are available for colorectal cancer screening, including tests that can detect cancers at an early treatable stage and tests that also detect pre-cancerous polyps and can lead to cancer prevention.
Guidelines from expert groups recommend that you and your healthcare provider discuss the available options and choose a testing strategy that is best for you. Tests that detect pre-cancerous polyps are preferable, such as colonoscopy and CT colonography. Stool tests that detect blood are another option. Although some tests are better than others, doing any test is better than doing nothing at all.
COLONOSCOPY: allows a physician to see the lining of the rectum and the entire colon. It requires that you prepare by cleaning out your entire colon and rectum. This usually involves consuming a liquid medication that causes temporary diarrhea. You are usually given sedation for the procedure. During colonoscopy, a thin, lighted tube is used to directly view the lining of the rectum and the entire colon. Polyps can be removed during this procedure.
Colonoscopy detects most small polyps and almost all large polyps and cancers. The risks associated with colonoscopy are greater than those with other screening tests. Colonoscopy may lead to serious bleeding or a tear of the intestinal wall in some individuals (about 1 in 1,000). Because the procedure usually requires sedation, you must be accompanied home after the procedure, and you should not return to work or other activities on the same day.
COMPUTED TOMOGRAPHY COLONOGRAPHY (CTC), sometimes called ‘virtual colonoscopy’, is a test that uses a CT scanner to take images of the entire bowel. Computer software is used to produce images in two and three dimensions to allow a radiologist to determine if polyps or cancers are present.
The major advantages of CTC are that it does not require sedation, it is non-invasive, the entire bowel can be examined and abnormal areas (polyps) can be detected about as well as with colonoscopy.
There are several disadvantages to CTC. Like traditional colonoscopy, CTC requires a bowel preparation to clean out the colon. If an abnormal area is found with CTC, a traditional colonoscopy will be needed at a later time to see the area and take a tissue sample. CTC may detect abnormalities other than polyps and colorectal cancer. Many of these incidental findings will require further testing. Like many other imaging tests, CTC exposes patients to radiation which may have long-term risks. In Canada CTC is not readily available and is usually only ordered in special situations by your Gastroenterologist.
Colorectal cancers often release microscopic amounts of blood and abnormal DNA into the stool. Stool tests can detect blood or abnormal DNA makers.
Fecal Occult Blood Testing (FOBT) Every Two Years. This method has been promoted by the Ontario government as part of its Colon Cancer Awareness Program. Samples of stool from three consecutive bowel movements are applied to home collection cards. These cards are tested by a laboratory for microscopic or occult blood; if the result is positive a colonoscopy is then performed to check for polyps or colon cancer. Studies show that doing an FOBT every two years reduced death from colorectal cancer by 16% over a decade.
Stool DNA Testing. This method involves collecting an entire bowel movement to be mailed to a laboratory with an ice pack. The stool DNA test evaluates stool for several DNA markers, which can be associated with colon cancers. This test is more sensitive than FOBT, but is not available in Canada.
COLON CANCER SCREENING PLANS
The recommended colon cancer screening plan depends upon your risk of colorectal cancer.
Average Risk of Colon Cancer
People with an average risk of colorectal cancer should begin screening at age 50. One of the following screening strategies is recommended:
Colonoscopy every 10 years or computed tomographic colonography every 5 years.
Fecal occult blood testing is an alternate option.
Increased Risk of Colon Cancer
Screening plans for people with an increased risk may entail screening at a younger age, more frequent screening, and/or the use of more sensitive screening tests (usually colonoscopy). The optimal screening plan depends upon the reason for increased risk.
Family History of Colorectal Cancer
People who have one first-degree relative (parent, brother, sister, or child) with colorectal cancer or polyps at a young age (before the age of 60 years), or two first-degree relatives diagnosed at any age, should begin screening for colon cancer earlier, typically at age 40, or 10 years younger than the earliest diagnosis in their family, whichever comes first. Screening usually includes colonoscopy, which should be repeated every five years.
People who have one first-degree relative (parent, brother, sister, or child) who has experienced colorectal cancer or precancerous polyps at age 60 or later should begin screening by colonoscopy at age 40, but instead of every 5 years they are usually followed every 10 years, unless precancerous polyps are found. In this happens they are then followed every 3-5 years depending on the size and number of polyps.
Some people have known genetically-based colon cancer syndromes in their family, such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colon cancer (HNPCC). These less common conditions require aggressive screening and preventive treatments, and individuals with these conditions in their family should be managed by a physician with clinical expertise in these syndromes.
Inflammatory Bowel Disease
People with Ulcerative Colitis or Crohn’s disease have an increased risk of colon cancer. The risk depends upon how much of the colon is affected and how long you have had the disease. The best screening plan usually is decided after discussion with your Gastroenterologist.
**Guidelines from expert groups recommend that you and your healthcare provider discuss the available options and choose a testing strategy that makes sense for you. While some tests are more effective than others, doing any test is better than doing nothing at all.