Screening for colon cancer

Posted 5/2/18

Colorectal (colon and rectal) cancer is the third most common type of cancer diagnosed, with prostate and lung cancer in males and breast and lung cancer for women being more common. Annually there …

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Screening for colon cancer


Colorectal (colon and rectal) cancer is the third most common type of cancer diagnosed, with prostate and lung cancer in males and breast and lung cancer for women being more common. Annually there are about 135,000 people diagnosed with bowel cancer and 50,000 related deaths.

This type of malignancy starts from the inner wall of the colon and can invade surrounding tissue and spread to other parts of the body. Tumors usually start out as benign polyps that over time can progress from pre-cancerous tumors to malignant growths.

Different from other types of malignancies, colorectal cancer is preventable and curable when found early. By removing pre-cancerous tumors before they invade through the wall of colon or spread to other parts of the body, it is estimated that it reduces the incidence of cancer by 90%. Because early colorectal cancer can have no symptoms, periodic screening is essential. This article will discuss various types of colon cancers and their risks of malignancy, screening methods and how often screening needs to be performed.

Importance of family history and cancer

For most of us who come from families who do not have a history of colorectal cancer or experience other risk factors, the overall risk of developing cancer is about 6% of the population. Family history of other members of the family with this cancer increases this risk significantly. (See table on page 13.)

There are also rarer hereditary bowel conditions that also increase the incidence of bowel cancer, like familial adenomatous polyposis (FAP) and Peutz-Jeghers syndrome. This type of condition occurs generally at earlier ages and requires intensive screening. Along with genetic conditions, inflammatory bowel diseases such as ulcerative colitis increases the risk of colorectal cancer. For individual with high-risk genetic colorectal diseases, genetic counseling and possible preventative bowel removal may be necessary.

Types of screening tests – pros and cons

Fecal occult blood testing (stool testing) is a general screening for blood in the stool. This involves testing three stool specimens collected on special cards. Prep is to avoid foods containing animal blood (steaks, hamburger), vitamin C, iron, aspirin and anti-inflammatory drugs for three days prior to collecting specimen.

Fecal immunochemical (FIT) is similar to fecal occult testing, except that you do not have to take dietary precautions. This is a more sensitive test for picking up the presence of blood mixed in the stool. It is more expensive and may not be covered by all insurance.

DNA testing is now available (Cologuard). It is more sensitive in picking up blood than FIT, but is not as specific in terms of identifying human blood from other sources.


If a person shows blood in the stool or is presenting for screening, a colonoscopy is performed and allows the physician to examine the entire length of colon for polyps and other growths in the bowel. This will require a 24-hour bowel prep in which the person consumes only clear liquids and then takes either pills, liquids, or laxatives. This completely empties the bowel allowing for clear visualization. Approximately half of polyps are found in the upper colon. For this reason, flexible sigmoidoscopies are now not generally used for screening, because they examine only about 1/3 of the lower portion of the colon.

There are now other tests being developed such as virtual colonoscopies that utilize a CT scanner to construct virtual images of the colon. There are some issues such as the fact that very small polyps or flat lesions cannot be identified, and it will not distinguish a small piece of stool from a polyp. Generally, if any abnormality is found or there is a clear polyp visualized the person still needs to undergo a colonoscopy for inspection and biopsy. This may, in the future, be used for follow up examinations for individuals with a history of polyps.

How often do you need to screen?

• The frequency of obtaining of colonoscopy depends on your overall risk of developing of colorectal cancer. For most people, the American Cancer Society (ACS) recommends a colonoscopy at age 50 and every seven to 10 years thereafter if the results are normal.

• If there are polyps or other abnormal findings, the interval for repeat testing is shorter. For individuals with a higher family history risk of cancer or inflammatory bowel disease, the recommended age of the initial procedure is often before the age of 50.

• The ACS recommends that people who have had small adenomas removed have a repeat colonoscopy at either a five- or 10-year intervals depending on personal and family medical history.

• If an individual had three to 10 adenomas removed, or if there was one large polyp removed, then the ACS recommends a repeat colonoscopy at three-year intervals.

• At any time, if the person is experiencing a change in bowel habits or sees blood in the toilet, it is essential that the individual seek out medical evaluation. 



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