Colon cancer prevention facts
Colon cancer often begins as a benign growth known as a polyp. It is recommended that most people have a screening colonoscopy every 10 years starting at age 50.
- Colon cancers maybe both preventable and, if detected, still curable if found at an early stage and promptly treated.
- Screening for colon cancer in asymptomatic people is recommended to begin at age 50.
- Risk factors for colorectal cancers include a family history of colon polyps, genetic factors, and certain lifestyle choices.
- Colonoscopy may treat and/or prevent colorectal cancers safely and effectively. Colon polyp removal is the most effective way to prevent colon cancer from occurring.
- The new Cologuard test also may detect early precancerous and/or cancers of the colon safely and effectively, and thus allow invasive colonoscopy to become more of a treatment modality instead of a "test and treat if necessary procedure."
- Treatments of patients to prevent colorectal cancer that may be effective in some individuals but may have long-term adverse side effects include any NSIAD therapy.
- The use of two antioxidants, vitamins A and C, are apparently ineffective in reducing the incidence of colorectal cancer.
- People with hereditary colon cancer syndromes should consider genetic testing
- Genetic testing and counseling can help determine the possibility of early-onset of colorectal cancers and allow early treatments.
- Lifestyle changes (high fruit/fiber diet, no smoking, weight loss, screening and genetic testing in some individuals) may help reduce and/or possibly even prevent some people from developing colorectal cancers.
Colon Cancer Screening And Surveillance
Screening recommendations for individuals with average risk of colon cancer
The life-time risk for an adult American to develop colorectal cancer is approximately 6%. Fecal occult blood tests and flexible sigmoidoscopic examinations are the recommended screening tests for these individuals at average risk for developing colorectal cancer.
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What measures to prevent colorectal cancer probably are effective but may have long term adverse side effects?
NSAIDs (nonsteroidal anti-inflammatory drugs) are widely used in the treatment of arthritis and other inflammatory conditions of the body. Some examples of NSAIDs include
aspirin, sulindac
(Clinoril), ibuprofen
(Advil, Motrin, Nuprin and others), naproxen
(Aleve, Naproxyn, Anaprox, Naprelan), and piroxicam
(Feldene). How NSAIDs prevent colon cancer and polyps is under investigation. (NSAIDs are potent inhibitors of prostaglandins in the body, and prostaglandins may be important in the formation of polyps.)
Why aren’t doctors recommending NSAIDs for colorectal cancer prevention? Because NSAIDs can cause stomach ulcers, intestinal bleeding and, sometimes, adverse effects on the liver and kidneys. Even though safer NSAIDs have been developed, doctors generally are reluctant to recommend aspirin or other NSAIDs for preventing
colorectal cancer until data on their effectiveness and long-term safety are available.
When prescribing an agent for prolonged periods of time to prevent a disease that may or may not occur, the last thing a doctor would want is for that agent to cause adverse side effects in a healthy person.
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Colon Cancer Prevention
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What measures to prevent colorectal cancer probably are effective and safe?
Oral supplements of calcium and folic acid, diets high in fruits and vegetables and low in saturated fat and red meat, avoiding obesity, regular exercise, and quitting cigarette smoking are safe measures that probably help to prevent colorectal cancer.
Calcium supplements have been shown in animal and human studies to decrease the number of pre-cancerous polyps. Fruits and vegetables contain many chemicals that inactivate cancer-causing chemicals (carcinogens). Obesity, a sedentary life style, cigarette smoking, and high red meat consumption have been linked to an increased risk of colorectal cancer. In a large study of nurses, those who took multivitamins that contained folic acid for decades had less colorectal cancer than women who did not take multivitamins.
These measures are considered only "probably" effective because long-term, large-scale, properly designed clinical trials have yet to be performed to establish conclusively that these measures actually prevent colorectal cancer.
Doctors are willing to prescribe an agent without conclusive proof of its effectiveness as long as it is safe. In many instances, conclusive proof may be many years away.
What prevention measures have been found to be ineffective?
Anti-oxidants are believed to have anti-cancer effects, but clinical trials using the anti-oxidant vitamins C and A has shown no benefit in preventing
colorectal cancer.
Many agents or measures that are promising because they have theoretical benefits fall short of expectations when subjected to rigorous clinical trials.
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What about genetic testing for colon cancer?
Genetic testing using blood tests are now available to identify patients with hereditary colon cancer syndromes. Hereditary colon cancer syndromes are caused by specific inherited mutations that are sufficient in themselves to cause colon polyps, colon cancers, and non-colonic cancers. Hereditary colon cancer syndrome can affect multiple members of a family. Approximately 5% of all colon cancers in the US are due to hereditary colon cancer syndromes. Patients who have inherited one of these syndromes have an extremely high risk of developing colon cancer. Fortunately, blood tests are now available to test for these hereditary colon cancer syndromes, once a syndrome has been suspected within a family.
Familial adenomatous polyposis (FAP)
Familial adenomatous polyposis or FAP is a hereditary colon cancer syndrome in which the affected family members develop large numbers (hundreds, sometimes thousands) of colon polyps starting in their teens. Unless the condition is detected and treated early (treatment involves removal of the colon), a family member with the FAP syndrome is almost sure to develop colon cancer. Cancers most commonly begin to appear when patients are in their 40's but can appear earlier. These patients also are at risk of developing other cancers such as cancers of the thyroid gland, stomach, and the ampulla (the part of the duodenum into which the bile ducts drain).
Attenuated familial adenomatous polyposis (AFAP)
Attenuated familial adenomatous polyposis or AFAP is a milder version of FAP. Affected patients develop less than 100 colon polyps. Nevertheless, they are at high risk of developing colon cancers at a young age. They are also at risk for stomach and duodenal polyps.
Hereditary nonpolyposis colon cancer (HNPCC)
Hereditary nonpolyposis colon cancer, or HNPCC, is a hereditary cancer syndrome in which affected family members tend to develop colon cancers, usually in the right colon, in their 30's to 40's. Certain HNPCC patients also are at elevated risk for developing uterine cancer, stomach cancer, ovarian cancer, cancers of the ureters (the tubes that connect the kidneys to the bladder), cancers of the bile ducts (the ducts that drain bile from the liver to the intestines), and cancer of the brain and skin.
MYH polyposis syndrome
The MYH polyposis syndrome is a recently discovered hereditary colon cancer syndrome. Affected patients typically develop 10-100 polyps during their 40's and are at high risk of developing colon cancer. The MYH syndrome is inherited in an autosomal recessive manner with each parent contributing one copy of the mutant gene. This results in one chance in four that their offspring may inherit both copies of the gene. Most people with the MYH syndrome do not have a multigenerational family history of polyps or cancer of the colon but may have brothers or sisters with it.
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Who should consider genetic counseling and testing?
Genetic counseling followed by genetic testing should be considered for individuals as well as their family members when there are:
- Individuals in the family with early onset of colon cancer, before age 50
- Individuals in the family with numerous colon polyps
- Families in which multiple members have colon cancer
- Families with members with numerous colon polyps
- Families with members having colon cancers at young ages
- Families with members having certain non-colon cancers such as cancers of the uterus, thyroid, ureters, ovaries, small intestine, etc.
Genetic testing without prior counseling is discouraged because of the extensive family education that is involved and the complicated nature of interpreting the test results.
Why is genetic counseling and testing important in hereditary colon cancer syndromes?
Patients who have hereditary colon cancer syndromes usually have no symptoms and are unaware that they have colon polyps or early colon cancers. They usually will develop colon cancers early in life (often before ages 40-50). Therefore, to prevent colon cancers in patients with hereditary colon cancer syndromes, colon screening must begin early. For example, patients with FAP should have annual flexible sigmoidoscopies starting at age 12, patients with AFAP should have annual colonoscopies starting at age 25, and patients with HNPCC should have colonoscopies beginning at age 25 (or 10 years younger than the earliest colon cancer diagnosed in the family, whichever is earlier). The current screening recommendations for the general population (fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy beginning at ages 40-50) are inadequate for most patients with hereditary colon cancer syndromes.
Genetic counseling and testing are important to identify patients and family members with hereditary colon cancer syndromes so that screening with flexible sigmoidoscopies and colonoscopies can begin early and, if necessary, the colon can be removed surgically to prevent colon cancer. Moreover, depending on which hereditary colon cancer syndrome is present, early screening for other types of cancer such as ovarian, uterine, stomach, ureter, and thyroid may be appropriate.
The screening role that the new Cologuard test may take is likely to be
determined in the near future.
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What can be done now to prevent colorectal cancer?
- Eat a diet high in fruits and vegetables and low in fat and red meat. (This diet also is good for cardio-vascular health.)
- Take oral calcium supplements and one multivitamin a day that contains 400 micrograms of folic acid. (Calcium supplements also are necessary for maintaining the strength of bones, and folic acid may be good for cardio-vascular health.)
- Lose excess weight, exercise regularly, and stop smoking cigarettes. (This also is good for cardio-vascular health.)
- Undergo screening tests for colorectal polyps and cancer. (Note that a new
test, Cologuard has been developed and approved by the FDA for home use.) - If one has family members with numerous colon polyps, early onset of colon cancers or other cancers such as uterine, stomach, thyroid, and ovarian cancer, talk to your doctor about genetic counseling and testing.
