Colon Cancer Screening and Prevention

Overview

Information about the prevention of cancer and the science of screening appropriate individuals at high-risk of developing cancer is gaining interest. Physicians and individuals alike recognize that the best "treatment" of cancer is preventing its occurrence in the first place or detecting it early when it may be most treatable.

Colorectal cancer is the second leading cause of cancer death in the United States. The disease strikes both men and women, with 130,000 cases diagnosed each year. Approximately 56,000 people die from colorectal cancer each year.

The chance of an individual developing cancer depends on both genetic and non-genetic factors. A genetic factor is an inherited, unchangeable trait, while a non-genetic factor is a variable in a person’s environment, which can often be changed. Non-genetic factors may include diet, exercise, or exposure to other substances present in our surroundings. These non-genetic factors are often referred to as environmental factors. Some non-genetic factors play a role in facilitating the process of healthy cells turning cancerous (i.e. the correlation between smoking and lung cancer) while other cancers have no known environmental correlation but are known to have a genetic predisposition. A genetic predisposition means that a person may be at higher risk for a certain cancer if a family member has that type of cancer.

Heredity or Genetic Factors

People with a personal or family history of adenomatous polyps or familial adenomatous polyposis (FAP) are at an increased risk for developing colorectal cancer. Adenomatous polyps are non-cancerous tumors that grow in the colon or rectum and become cancerous, ultimately developing into colorectal cancer. Familial adenomatous polyposis (FAP) is a genetic disease that causes hundreds of adenomatous polyps to form in the colon or rectum. FAP most often affects adolescents and young adults, many of whom develop colorectal cancer at an early age.

Hereditary nonpolyposis colorectal cancer (HNPCC) is a genetic syndrome caused by mutation in one of several genes. HNPCC accounts for about 3-5% of all colorectal cancer. With HNPCC, people develop a single colorectal cancer rather than an unusual number of polyps, as in FAP. Individuals with the HNPCC gene mutations have an 80% lifetime risk of developing colorectal cancer.

Individuals with a family history of colorectal cancer or colorectal adenomas (polyps) also have an increased risk of developing colorectal cancer, as do those with a personal history of either of these conditions. In addition, people suffering from inflammatory bowel disease have a greater chance of developing colorectal cancer. Research indicates that the presence of a gene called the pituitary tumor transforming gene (PTTG) may help to identify colon polyps most at risk for becoming cancerous.

Environmental or Non-Genetic Factors

About 75% of all new cases of colorectal cancer occur in people who have no known risk factors other than age. Research indicates that the risk for colorectal cancer increase substantially after age 50.

Diet: Some, but not all, research indicates that a high-fat diet, as well as a diet low in fiber and folic acid, may play a role in the development of colorectal cancer. Three recently published clinical studies, however, have failed to produce evidence to support the theory that a diet low in fiber leads to colorectal cancer. There is considerable evidence, however, that a high intake of red meat increases the risk of colorectal cancer.

In a study involving 76,402 women, researchers at the Harvard School of Public Health in Boston found that a “western” diet increases the risk of colon cancer, compared to a “prudent” diet. A “western” diet was defined as including higher levels of red and processed meats, sweets and desserts, French fries, and refined grains while the “prudent” diet consisted of higher intakes of fruits, vegetables, legumes, fish, poultry and whole grains. After the data was adjusted for additional risk factors (which can skew statistical results), the researchers reported that women on a Western diet were 46% more likely to develop colon cancer than women who ate a prudent diet.[1]

Obesity also appears to influence the development of polyps and their progression to malignancy. The reason for the relationship between obesity and colon cancer remains unknown; however, some researchers have theorized that elevated insulin may be a factor.

Smoking: The use of alcohol and tobacco in combination has been linked to the risk of developing colorectal cancer. A recent study by the American Cancer Society (ACS) indicates that long-term smoking may significantly increase the risk of colorectal cancer. The ACS researchers examined 14 years of data (1982-1996) collected from the Cancer Prevention Study II (CPS II). They evaluated the smoking patterns of 312,332 men and 469,019 women as reported by these participants when they entered the study in 1982. The researchers found that colorectal cancer death rates were highest among current smokers, intermediate among former smokers and lowest among never smokers. The risk of dying from colorectal cancer was higher among those who smoked for 20 or more years.

The duration and amount of smoking was a significant factor, as the data showed that the risk of colorectal cancer increased with the number of cigarettes smoked daily and the number of years of smoking. A younger age at initiation also increased the risk. On the other hand, the colorectal cancer risk decreased with each year after quitting smoking. The data also showed that cigar and pipe smokers had an increased risk of colorectal cancer as well.

Since the data showed that the risk of dying from colorectal cancer increased with the duration and amount of smoking, the researchers concluded that there might be a causal relationship between smoking and colorectal cancer. If this causal relationship does indeed exist, then approximately 12% of colorectal cancer deaths in the U.S. in 1997 were attributable to smoking.

Prevention

Cancer is largely a preventable illness. Two-thirds of cancer deaths in the U.S. can be linked to tobacco use, poor diet, obesity, and lack of exercise. All of these factors can be modified. Nevertheless, an awareness of the opportunity to prevent cancer through changes in lifestyle is still under-appreciated.

Because colorectal cancer is a highly curable disease when detected early, the best form of prevention is screening and early detection. When an adenomatous polyp, which is a precursor lesion, develops, it takes 10 to 15 years to transform into cancer; therefore, people with an increased risk for developing colorectal cancer may want to undergo screening at a younger age and continue with screening frequently in an attempt to prevent this development. Several screening programs may be used to detect early stage colorectal cancer and polyps. These polyps can then be removed, thereby preventing the development of colorectal cancer.

Diet: Diet is a fertile area for immediate individual and societal intervention to decrease the risk of developing certain cancers. Numerous studies have provided a wealth of often-contradictory information about the detrimental and protective factors of different foods.

There is convincing evidence that excess body fat substantially increases the risk for many types of cancer. While much of the cancer-related nutrition information cautions against a high-fat diet, the real culprit may be an excess of calories. Studies indicate that there is little, if any, relationship between body fat and fat composition of the diet. These studies show that excessive caloric intake from both fats and carbohydrates lead to the same result of excess body fat. The ideal way to avoid excess body fat is to limit caloric intake and/or balance caloric intake with ample exercise.

It is still important, however, to limit fat intake, as evidence still supports a relationship between cancer and polyunsaturated, saturated and animal fats. Specifically, studies show that high consumption of red meat and dairy products can increase the risk of certain cancers. One strategy for positive dietary change is to replace red meat with chicken, fish, nuts and legumes.

High fruit and vegetable consumption has been associated with a reduced risk for developing at least 10 different cancers. Some researchers believe that this may be a result of potentially protective factors such as carotenoids, folic acid, vitamin C, flavonoids, phytoestrogens and isothiocyanates, often referred to as antioxidants.

For many years, researchers speculated that the low incidence of colorectal cancer in parts of Africa could be linked to a high-fiber diet; however, several studies have failed to support this theory. In 1999, three pivotal clinical studies evaluating the effects of a high-fiber diet on colorectal cancer failed to establish a correlation between high fiber consumption and reduction in the incidence of colorectal cancer. In two of these studies, researchers directly compared 2 groups of individuals with either high or low fiber consumption and found an equal number of polyps in each group. There are many reasons to eat a diet high in fiber, particularly to help reduce the risk for coronary artery disease; however, such a diet does not appear to help prevent the development of colorectal polyps or cancer.

There is strong evidence that moderate to high alcohol consumption also increases the risk of certain cancers. One reason for this relationship may be that alcohol interferes with the availability of folic acid. Alcohol in combination with tobacco creates an even greater risk.

Exercise: Higher levels of physical activity may reduce the incidence of some cancers. According to researchers at Harvard, if the entire population increased their level of physical activity by 30 minutes of brisk walking per day (or the equivalent energy expenditure in other activities), we would observe a 15% reduction in the incidence of colon cancer.

A group of Swiss researchers compared the physical activity levels of 223 individuals with colorectal cancer and 491 individuals without colorectal cancer. The results indicated an increased that individuals with a sedentary lifestyle have an increased risk of developing colorectal cancer. This association was present regardless of age, gender, weight or alcohol intake. Although there is no sure way to prevent any cancer from developing, these researchers concluded that increasing one’s level of physical activity may help to prevent one-fifth to one-third of all colorectal cancer cases.

Celecoxib: Research has indicated that a non-steroidal, anti-inflammatory drug called Celecoxib may reduce the number of polyps that develop in patients with FAP, thus significantly reducing their risk for developing colorectal cancer. The FDA has approved this drug to be used for treatment of individuals with FAP. Clinical studies will be ongoing to determine if other high-risk individuals can benefit from Celecoxib.

Statins: A large study presented at the 2004 meeting of the American Society of Clinical Oncology showed that the use of statins (cholesterol-lowering drugs) for 5 years or more is associated with a 46% reduction in the risk of colorectal cancer. This rate was adjusted for other known risk factors such as age, physical activity, and diet.[2]

Screening and Early Diagnosis

For many types of cancer, progress in the areas of cancer screening and treatment has offered promise for earlier detection and higher cure rates. The term screening refers to the regular use of certain examinations or tests in persons who do not have any symptoms of a cancer but are at high risk for that cancer. When individuals are at high risk for a type of cancer, this means that they have certain characteristics or exposures, called risk factors that make them more likely to develop that type of cancer than those who do not have these risk factors. The risk factors are different for different types of cancer. An awareness of these risk factors is important because 1) some risk factors can be changed (such as smoking or dietary intake), thus decreasing the risk for developing the associated cancer; and 2) persons who are at high risk for developing a cancer can often undergo regular screening measures that are recommended for that cancer type. Researchers continue to study which characteristics or exposures are associated with an increased risk for various cancers, allowing for the use of more effective prevention, early detection, and treatment strategies.

Screening is crucial for the prevention and early treatment of colorectal cancer. It is currently recommended that all patients over age 50 be screened regularly for colorectal cancer. Additionally, people with a personal or family history of adenomatous polyps, FAP, HNPCC, or colorectal cancer may begin screening much earlier.

Several screening strategies are currently available. These include the fecal occult blood test (FOBT), flexible sigmoidoscopy, colonoscopy and double contrast barium enema. It is currently recommended that patients begin receiving an annual fecal occult blood test (FOBT) at age 50 and a flexible sigmoidoscopy every 5 years after age 50. It is also recommended that a colonoscopy be performed every 10 years, and if the FOBT is positive or if adenomas are found during the sigmoidoscopy. Some physicians also recommend that a double-contrast barium enema be performed every 5 to 10 years after age 50, however, current research indicates that the colonoscopy may be a more effective screening procedure. Individuals interested in colorectal cancer screening should discuss the options with their physician in order to determine the most appropriate procedure.

Fecal Occult-Blood Test (FOBT): The fecal occult-blood test checks for hidden blood in the stool. Recently, results from an 18-year study indicated that annual or biannual FOBT could significantly reduce the incidence of colorectal cancer. This test indicates the presence of bleeding polyps and thereby indicates a need for further screening. This follow-up screening allows for both the identification and removal of polyps, which results in a reduced incidence of colorectal cancer.

Flexible sigmoidoscopy: During this procedure, a physician uses a lighted tube to look inside the rectum and the lower part of the colon (sigmoid colon) for polyps or areas suspicious for cancer. The physician may perform a biopsy in order to collect samples of suspicious tissues or cells for closer examination. This is an outpatient procedure that does not require sedative anesthesia or pain medication. There are no or few complications associated with this procedure.

Colonoscopy: During this procedure, a longer flexible tube that is attached to a camera is inserted through the rectum, allowing physicians to examine the internal lining of the colon for polyps or other abnormalities. The physician may perform a biopsy in order to collect samples of suspicious tissues or cells for closer examination. This is a more difficult procedure than sigmoidoscopy requiring anesthesia or heavy sedation. Significant complications occur 1% of patients or less.

Double-contrast barium enema: A chalky substance called barium is inserted through the rectum and into the colon and rectum. The patient then undergoes x-rays of the colon and rectum so that the physician can evaluate the area for polyps or other abnormalities. The barium helps open the colon so that the x-rays are more detailed and clear.

While these screening strategies help to monitor for the development of adenomatous polyps and colorectal cancer, other tests exist which may allow physicians to identify patients who are at risk for the development or recurrence of colorectal cancer.

Carcinoembryonic antigen (CEA): The CEA test is designed to identify cancer cells in the patient’s blood by recognizing a specific protein that is found on the surface of these cells, called the CEA. The CEA test is not currently utilized for screening purposes because it is a non-specific test, which means that the presence of CEA could be an indicator of any of a number of conditions. The presence of CEA in the blood appears to be a useful indicator to identify patients at high risk for recurrence after standard treatment for colorectal cancer.

Predictive genetic testing: A predictive medicine test for hereditary colorectal cancer is now available. This test detects disease-causing mutations in two genes, MLH1 and MSH2, which are responsible for the majority of hereditary non-polyposis colorectal cancer (HNPCC). This test may allow patients who are identified to be at a high risk for HNPCC to have earlier and more frequent exams and to have pre-cancerous polyps removed. Individuals interested in genetic testing should consult with their physicians about the risks and benefits of this procedure.

Research is ongoing to develop and refine the optimal screening programs for individuals at risk of developing colorectal cancer.

Strategies to Improve Screening and Early Detection of Colon Cancer

The potential for earlier detection and higher cure rates increases with the advent of more refined screening techniques. In an effort to provide more screening options and perhaps more effective prevention strategies, researchers continue to explore new techniques for the screening and early detection of cancer.

Several new strategies for the screening of colorectal cancer have recently emerged. Despite progress in this area, it is still important that individuals continue to utilize the standard screening procedures in an effort to maintain health and detect colorectal cancer early when it is most treatable. However, these new procedures hold promise for earlier and more reliable detection of colorectal cancer and some individuals may be interested in participating in clinical trials that will help to determine the effectiveness of these new techniques.

DNA stool test: This new screening procedure involves looking for abnormal DNA in stool samples. Changes in DNA occur as tumors develop in the colon. The tumors shed cells into the intestine, which makes it possible to detect the abnormal DNA cells in stool samples. This simple, non-invasive screening procedure has proven effective in clinical studies. Research is ongoing to determine the feasibility of using this as a standard screening procedure.

Virtual colonoscopy: In virtual colonoscopy, spiral CT scanners scan the entire colon to produce a 3-D image. The procedure allows for the complete visualization of the colon more quickly and less invasively than with conventional colonoscopy. While this is a promising new technique, more research will be needed to refine the procedure before it becomes a standard screening procedure for colorectal cancer. This procedure may evolve as technology continues to improve.

The above-mentioned techniques are new areas of exploration in the screening and early detection of colorectal cancer. Clinical trials are being utilized to determine the efficacy of these procedures. While the results look promising and the implications could be exciting, these procedures are not yet the standard. It is imperative that individuals continue to utilize the existing methods of screening for colorectal cancer in order to ensure early detection.

References

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