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Colorectal Cancer: Why Is Screening Important?

I Introduction
II What is Colorectal Cancer?
III Who Is At Risk?
IV Available Screening Tools
V Preventive Efforts
VI Applications to Practice

--Karen Parsons, MSc (App), RD, Study Coordinator for Colon Cancer Screening Study at Sunnybrook and Women's College Health Sciences Centre

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I Introduction

Colorectal Cancer (CRC) is the second most common cancer killer in Canada in both men and women (National Cancer Institute of Canada, 1998). In 2003, there were an estimated 8,300 deaths and 18,000 newly diagnosed cases (National Cancer Institute of Canada, 2003). Canada has one of the highest CRC incidence rates in the world (National Cancer Institute, 1998). Therefore, individuals working in the Canadian healthcare setting need to stimulate and encourage discussion about CRC and the need for screening.

II What is Colorectal Cancer?

Early detection is the key to preventing CRC and producing better survival. This is primarily due to the development of this particular cancer within the colon. Over 90% of CRC cases develop from benign growths called polyps that grow on the lining of the colon. As the polyp grows and progresses, it may form pre-cancerous cells that will
eventually progress to a cancer (Loren et al, 2002). This entire process takes approximately 10 years. If CRC screening occurs during this time and the polyps are detected and removed, the cancer can be prevented.

Symptoms appear only in the later stages of these cancers, and even then symptoms are often vague. Symptoms include: rectal bleeding, change in bowel habits, diarrhea, unexplained weight loss greater than 10% in past six months and abdominal pain (Loren et al, 2002). If routine screening is not performed, the polyp or cancer will remain undetected, thus reducing the chances for survival.

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III Who Is At Risk?

The incidence of CRC increases after the age of 50 in both men and women. If a person is at average risk for CRC, s/he should be screened after the age of 50 (OGAG, 2002). Screening is not recommended before 50 years due to the low incidence of CRC before this age (Imperiale et al, 2002).

Family history of colon cancer is strongly related to an elevated risk of colon cancer (Canadian Task Force, 2001). Persons with a first-degree relative (parent, sibling or child) diagnosed with CRC have a two- to three-fold increased risk. If an individual has two first-degree relatives diagnosed with colon cancer, there is a three- to four-fold risk (Winawer et al, 2003).

There are hereditary and specific genetic disorders that can elevate one's risk for CRC, but these are less common (Loren, 2002). In these cases, CRC screening should start at a younger age compared to an average at-risk person.

Persons with inflammatory bowel disease (ulcerative colitis or Crohn's disease) are at increased risk for CRC. Even if these people do not have a family history of CRC, they should still be screened before 50 years of age (OGAG, 2002).

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IV Available Screening Tools

The type of screening recommended for an average risk person includes (Canadian Task Force, 2001; OGAC, 2002; American Gastroenterological Association, 2003):
* Fecal Occult Blood Testing (FOBT) on an annual or biennial basis (testing for blood in the stool)
* Flexible Sigmoidoscopy every five years (examination of the first 60 cm of the colon using video technology) either alone or in combination with an annual FOBT

There is less conclusive evidence that the following methods provide an added benefit for those individuals who are at average risk:
* Double-Contrast Barium Enema every five years (examination of the entire colon using x-ray)
* Colonoscopy every ten years (examination of the entire colon using video technology)

The colonoscopy is the most sensitive screening tool of all four tests as polyps can be removed and abnormal areas biopsied. However this procedure involves greater risk to the patient and may be inconvenient. These concerns need to be discussed with a specialist.
Other screening methods are being developed but are not currently recommended as the sole screening method in average at-risk individuals due to insufficient evidence proving their effectiveness. These other methods include:
* Genetic testing
* "Virtual" colonoscopy (or CT colonography)

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V Preventive Efforts

Certain lifestyle choices can aid CRC prevention. CRC rates are highest in westernized countries and migrant studies have shown that rates of CRC rise when immigrants move to North America (Gatof, 2002). This occurs due to changes in diet and activity patterns. Some behaviors that can reduce one's risk of CRC are to stop smoking, maintain a healthy weight, exercise on a regular basis, and follow a diet that is high in fruits and vegetables and low in fat and processed or red meats (Gatof, 2002). The benefit of fruits and vegetables is that they are high in soluble and insoluble fiber and folate. A high calcium intake through supplements or diet has also shown a protective effect (Loren et al, 2002). A multivitamin containing calcium and folate can help to meet daily requirements, as it can be difficult to meet recommended levels by diet alone.

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VI Applications to Practice

Since CRC is a highly preventable disease, it is important to get screened. Even a one-time screen at age 55 with either a sigmoidoscopy or a colonoscopy can help to decrease CRC mortality by up to 50% (Fraizer et al, 2000; OGAC, 2003).

Healthcare providers need to encourage discussion regarding CRC screening with their patients above the age of 50, regardless of gender or risk level. When discussing screening, risks and benefits need to be communicated, as well as the availability of the different screening methods and the preferences of the patient. Apart from family physicians, people who work in the area of health prevention and promotion can also help to increase awareness about colorectal cancer. Encouraging people to talk (and even laugh) about this health issue will help to break down the stigma associated with screening and colorectal cancer--and even help to save lives.

VII References

Report of the Ontario Expert Panel on Colorectal Cancer Screening. 2003. Accessed April 15, 2003.

Canadian Cancer Society. Population-based colorectal cancer screening: position statement. Toronto: The Society; 2003. Accessed April 15, 2003.

Fraizer, A.L., Golditz, G.A., Fuchs, C.S., Kuntz, K.M Cost-effectivenes of Screening for Colorectal Cancer in the General Population. JAMA 2000:284;1954-1961.

Gatof, D., Ahnen, D. Primary prevention of colorectal cancer: diet and drugs. Gastroenterology Clinics of North America 2002:31;587-623.

Harvard Report on Cancer Prevention. Volume 3: Prevention of colon cancer in the United States 1999:10;167-180.

Imperiale, T.F., Wagner, D.R., Lin, C.Y, Larkin, G.N, et al. Results of Screening Colonoscopy Among Persons 40 to 49 Years of Age. New England Journal of Medicine 2002;346:1781-5.

Katz, J., Reynolds, J.C. The early diagnosis and prevention of gastrointestinal cancer: problems and promises. Gastroenterology Clinics of North America 2002:31;369-378.

Kronborg, O., Fenger, C., Olsen, J., Sondergaard, O. Randomized study of screening for colorectal cancer with faecal-occult-blood test. The Lancet 1996:348;1467-71.

Loren, D., Lewis, J., Kochman, M. Colon cancer: detection and prevention. Gastroenterology Clinics of North America. 2002:31:565-586.

National Cancer Institute of Canada. Canadian Cancer Statistics 2003. Toronto: The Society: 2003. p.18. Accessed November 24, 2003.

National Cancer Institute of Canada. International Comparisons 1998. Toronto: The Society: 2003. Accessed December 10, 2003.

Ontario Guidelines Advisory Committee. Recommended Clinical Guidelines 2002. Accessed April 15, 2003.

Winawer, S., Fletcher, R., Rex, D., Bond, J., et al. Colorectal Cancer Screening and Surveillance: Clinical Guidelines and Rationale - Update Based on New Evidence. Gastroenterology 2003;124:544-560.