Screening for Cancer of the Colon or Rectum
Frederick R. Jelovsek MD
Colorectal cancer is a leading cause of cancer deaths and the most common gastrointestinal malignancy. The lifetime risk of colon and rectal cancer is 6-7% and it increases sharply after age 50. Many women are not aware that their chance of getting colorectal cancer is about 5 times greater than of getting ovarian cancer. For someone interested in living a long life, it would be wise to know how to be screened to pick up colorectal cancer in its earliest stages.
In a recent continuing medical education article, Early DS: Colorectal cancer screening: An overview of available methods and current recommendations. South Med J. 1999; 92:258-265, we are presented with a good overview of how to go about screening for this devastating cancer.
How does cancer of the colon develop?
The skin lining the colon (mucosa) sometimes undergoes a transition from normal to glandular hyperplasia (adenomatous polyps) to cancerous tissue in a stepwise fashion over a 5-15 year time period. Nearly all colon cancers arise from these adenomatous polyps. The opposite is not true, however, that all polyps develop into cancer. In fact most polyps of the colon do not become cancerous, but their existence is a risk factor. There is one exception to this normal-adenomatous polyp-cancer progression and that is in ulcerative colitis in which the cancers are preceded by a different process, a dysplasia or non-polypoid abnormal growth pattern. Thus in most cases, if adenomatous polyps can be detected and removed, that may help prevent colon cancer.
What different diagnostic tests are available to detect colon or rectal cancer?
The basic tests available to screen for colorectal cancer are flexible sigmoidoscopy, checking the stool for hidden blood (fecal occult blood), dye and air in the colon (air contrast barium enema), and looking beyond the lower part of the colon (sigmoid) into the transverse and ascending colon using a scope called colonoscopy.
Approximately 50-65% of colon cancers occur in the lower part of the colon that is visualized with a flexible sigmoidoscopy. Studies have shown that sigmoidoscopy is associated with a 59-79% reduction in cancer mortality. Checking the stool for blood is considered a cancer test because a polyp would need to be fairly large sized in order to bleed. In other words, looking in the colon will pick up polyps sooner than waiting for them to grow big enough to bleed. Fecal occult blood tests have been shown to reduce colon cancer by about 33%. Air contrast barium enema can pick up more lesions than sigmoidoscopy but is not as good as colonoscopy. If the barium enema is abnormal, a colonoscopy has to be done anyway so this is not as cost effective as a screening test. Colonoscopy is a more sensitive test to find polyps and cancer but it is more expensive and occasionally patients have serious complications (3-17/1000) or even death (2/10000). It is used for screening women who are at high risk or who have a positive fecal occult blood test.
What are the screening tests recommended for a woman at average risk of colon cancer?
Starting at age 50, it is recommended that women have a yearly fecal occult blood screen and a flexible sigmoidoscopy every 5 years or a total colon exam ( barium enema or colonoscopy) every 5-10 years.
What would make a woman at higher than normal risk for colorectal cancer?
If a woman has had a history of having adenomatous polyps or a past colon cancer, a history of inflammatory bowel disease (ulcerative colitis, regional enteritis), or a strong family history of colorectal cancer or adenomatous polyps, then she should be considered at high risk.
Having had a colorectal cancer, there is an increased risk of a second colorectal cancer of about 6% over an 18 year period. Over a third of women in whom colon polyps have been detected and removed have a recurrence of the polyps. If there is a family history of polyposis or colon cancer, there may be a genetic tendency toward colon cancer. This needs to be investigated and sometimes genetic testing will have to be performed even though a genetic tendency only explains about 5% of colorectal cancers.
Should a woman at high risk for colorectal cancer be followed or screened differently than a woman at average risk?
Briefly, yes. The table below gives Early's recommendations:
Colorectal Cancer Screening in High Risk Individuals
|Risk Factor||Screening Test||Frequency|
|history of colorectal cancer||colonoscopy||every 1-3 years|
|history of adenomatous polyps||colonoscopy||every 3 years|
|history of inflammatory bowel disease||colonoscopy||every 1 to 2 years, after 8-10 years of extensive colitis (right and left) or after 15 years of left sided colitis|
|family history of colorectal cancer or adenomatous polyps|
|first degree relative||fecal occult blood test,
every 3-5 years starting at age 40
|two first degree relatives
(or young age at diagnosis
|fecal occult blood test,
every 3-5 years starting at age 40
or at 10 years younger than the youngest case
|hereditary nonpolyposis colorectal cancer||colonoscopy||at 5 years younger than the youngest case in the family or at age 25, then every 1 to 2 years|
|familial adenomatous polyposis||flexible sigmoidoscopy||at age 12 then yearly|
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What Does a Positive Fecal Occult Blood Test Mean?