Colon Cancer Prevention

Cancer of the colon and the rectum (also known as colorectal cancer) is a malignant growth arising from the inner lining of the colon or rectum. Colorectal cancer is the third leading cause of cancer for both sexes in the United States. The American Cancer Society report estimates that more than 106,000 cases will be diagnosed in 2024 and over 53,000 deaths due to colorectal cancer will occur in 2024.

Colorectal cancer is a major cause of cancer-related deaths among men and women in the United States.

The good news is that colorectal can be both curable and preventable - if it is detected early and completely removed before the cancerous cells metastasize (spread) to other parts of the body. Colorectal cancer can be prevented by removing colorectal polyps before they grow and change into cancers, or by using natural substances or man-made chemicals to prevent the colorectal polyps from changing into cancer. (Using natural substances or chemicals to prevent cancer is called chemoprevention).

Measures to prevent diseases usually fall into one of five categories of safety and effectiveness. These categories are:

1. Measures that have scientifically-proven effectiveness and long-term safety
2. Measures that probably are effective but may have long-term, adverse side effects
3. Measures that probably are effective, and safe
4. Measures that have been found to be ineffective or unsafe
5. Measures that have no scientific basis and no studies to measure effectiveness and safety

Screening for colorectal cancer is one of the best ways to prevent the disease. Colon cancer screening tests and procedures look for pre-cancerous or cancer cells in people who have no symptoms of disease.

Screening procedures and tests as well as schedules of screening tests may vary depending on a person's risk factors. Adults who have no risk factors for colon cancer should begin colon screening at the age of 45, according to the American Cancer Society.

Currently available methods for screening for colorectal cancer include the stool-based tests and visual examinations. The simplest tests are the stool-based tests. They examine a sample of stool for the presence of blood, since colorectal cancer often causes bleeding. These tests are known as FIT (fecal immunochemical test) or guaiac-based fecal occult blood test (gFOBT). These tests are easier to do but need to be done more often. If the result is abnormal, a visual examination must be done.

In addition to tests that look for blood in the stool, the FDA-approved Cologuard test is a non-invasive stool test that detects abnormalities in DNA fragments. The test has been proved safe and effective in a large clinical trial. It is less expensive and much easier to accomplish than colonoscopy but it is not a treatment procedure.

Visual examinations to screen for colorectal cancer include sigmoidoscopy and colonoscopy. Unlike stool-based tests, visual tests can both screen for precancerous and cancerous conditions and treat many of those (by removing the suspected tissue) during a single invasive procedure. Colonoscopy is typically preferred because it can examine the entire colon, while sigmoidoscopy only examines about one-third of the colon (the rectum and sigmoid).

A number of researchers and companies are currently developing blood-based tests that are designed to detect cancers including colon cancer in the early stages.

Age: Most cases of colorectal cancer occur in people over the age of 50, but in recent years there has been an increasing incidence of the condition in younger people as well.

Family history: People who have a family history or other risk factors for colon polyps, cancer, or IBD (inflammatory bowel diseases like ulcerative colitis and Crohn's disease) have an increased risk and should discuss screening ages and options with their doctor.

A genetic syndrome: Certain conditions, including Familial Adenomatous Polyposis (FAP) or hereditary non-polyposis colorectal cancer (Lynch syndrome) increase the risk for developing colorectal cancer (see below).

Those with a positive family history or diagnosed with a genetic syndrome should begin testing to look for possible early colon cancer at a younger age. This should be discussed with their doctor.

Medical conditions: People with type 2 diabetes have an increased risk for developing colorectal cancer independent of obesity and lifestyle risk factors.

Racial and ethnic background: The highest rates of colorectal cancer in the US are found in American Indian and Alaska Native people, followed by Black men and women. Worldwide, Jews of Eastern European descent (Ashkenazi Jews) have one of the highest colorectal cancer risks of any ethnic group. 

Lifestyle factors: Several lifestyle factors are believed to increase the risk of colorectal cancer including:

• Obesity
• Alcohol use
• Cigarette smoking
• Sedentary lifestyle (lack of regular physical activity)
• A diet low in fiber and high in fat and red meat

Colonoscopy and flexible sigmoidoscopy, along with digital rectal examination and stool occult blood testing, are the primary and most important tools for both preventing colorectal cancers and detecting early colorectal cancers.

Most colorectal cancers arise from colorectal polyps (small growths on the inner lining of the colon and the rectum). Even though colorectal polyps are initially benign, they can grow and change into colorectal cancers over a period of time ranging from five to twenty years. A large study that was conducted in several research centers in the United States showed that patients who had their polyps removed (usually via colonoscopy) had a 76% to 90% decrease in colorectal cancer.

Early detection and subsequent treatment of abnormal cells or structures (polyps and/or adenomas) can be precancerous or early signs of colon cancer. If these cells and structures are detected and removed by colonoscopic procedures, many colon cancers can effectively be prevented or stopped. 

Colon cancer prevention

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, ibuprofen, naproxen, and piroxicam. 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.

Safe and effective prevention

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, alcohol use, 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 recommend 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?

Antioxidants 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.

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.

1. 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. Individuals with this condition typically should begin screening for colorectal cancer at age 11. 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). FAP causes about 1% of all colon cancers.

2. 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.

3. 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. This condition causes 2-4% of colon cancers. 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.

4. 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.

Who should consider genetic counseling and testing?

Genetic tests of a blood or saliva sample are available to test for alterations in genes that cause the hereditary colon cancer syndromes. In recent years there has been an observed increased incidence of colorectal cancer among individuals younger than 50 years of age. Further, a number of people with this condition who have heritable genetic mutations remain undiagnosed under past genetic testing guidelines, which limited testing to specific age groups and forms of cancer. The U.S. National Comprehensive Cancer Network (NCCN) has announced new guidelines that recommend germline multigene panel testing for all individuals under 50 years of age with colorectal cancer as well as consideration for this testing for those with a family history of CRC or certain genetics signals in their tumor tissue.

Genetic counseling followed by genetic testing is particularly important 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 screening?

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. The current screening recommendations for the general population (fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy beginning at ages 45) 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.