• Why screen for colon cancer?
• How can screening prevent colon cancer?
• How do we screen for colon cancer and polyps?
• What is the best screening test for colon cancer?
• What about other tests?
• What does PAMF recommend?

Why screen for colon cancer?

The colon, or large intestine, is the last portion of the gastrointestinal tract and ends with the rectum. Cancer of the colon is the second most frequent cause of death from cancer in the United States, resulting in about 57,000 deaths per year. The risk of colon cancer increases as people age – 90 percent of colon cancers occur in individuals over 50 years of age.

Colon cancer is also more common in people with a family history of colon cancer, or a personal history of colon polyps or inflammatory bowel disease. Cigarette smoking and excessive alcohol consumption may also increase the risk of colon cancer. The good news is that early screening can lead to both prevention of and better cure rates for colon cancer.
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How can screening prevent colon cancer?

Colon cancer develops slowly, over about 10 years, from growths called polyps. Though most polyps remain benign (not cancerous), some can become pre-cancerous. Fortunately, removal of polyps with pre-cancerous changes can prevent cancer from developing in those polyps.

Polyps that have developed early cancer can also generally be cured by removal. Many polyps and early cancers cause no symptoms. Therefore, it is essential to detect them by the screening methods described below. More advanced polyps or cancers may cause visible blood in the stool, persistent change in the stool shape or size, or abdominal pain.
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How do we screen for colon cancer and polyps?

There are two major ways to screen for colon cancer.

• Fecal Occult Blood Testing
  
• Endoscopy

1. Fecal Occult Blood Testing (FOBT), also known as stool test cards or "Hemoccult" cards, is the first way to screen for colon cancer.

FOBT detects bleeding from polyps or cancers that might occur in amounts too small to be visible. Small stool samples are collected at home and placed onto cards that are returned to the laboratory. Patients taking the test must follow the directions carefully, as the test result can be affected by certain foods, medications and vitamins.

Research has shown that annual screening with the fecal occult blood test reduces colon cancer deaths by up to 33 percent. However, FOBT alone is not a sufficient screening test, since not all polyps and cancers bleed, or some bleed from time to time and may be missed during the three days of the test, giving a “false negative” result. On the other hand, benign conditions like hemorrhoids may bleed, producing “false positive” results. False positive results may cause anxiety and unnecessary follow-up testing. Nevertheless, because up to 25 percent of positive FOBT results are caused by cancer or pre-cancerous polyps, we strongly recommend further testing with colonoscopy (see below) when blood is found.

2. Endoscopy is the second way to screen for colon polyps and cancer.

A physician inserts a flexible fiberoptic tube through the rectum to examine the colon. There are two options for endoscopy: flexible sigmoidoscopy and colonoscopy.

Flexible sigmoidoscopy uses a flexible fiberoptic tube about one half inch (1 cm) in diameter and about two feet long (60-70 cm). A physician or other practitioner examines the lining of the lower half (left side) of the colon. If any growths are found, tiny pieces can be removed painlessly (biopsied) and sent to the laboratory for examination under the microscope.

Studies show that sigmoidoscopy lowers colon cancer deaths by 70 percent for cancers found within reach of the scope. Flexible sigmoidoscopy is done in the physician’s office, takes about 10 minutes and involves minor preparation: a clear liquid diet, a laxative and an enema at home before the procedure. No sedation is needed for the procedure. Unfortunately, flexible sigmoidoscopy cannot reach the upper half (right side) of the colon and so polyps or cancers in that part of the colon remain undetected.

Combining annual fecal occult blood testing and periodic flexible sigmoidoscopy may be more accurate than either test alone. If stool test cards are positive for blood, or sigmoidoscopy detects a polyp or other abnormality in the lower colon, colonoscopy is usually recommended to examine the rest of the colon.

Colonoscopy is the most thorough screening test for colon cancer. Colonoscopy differs from sigmoidoscopy in several important ways.

First, the scope used is much longer (about 5 feet or 152 cm), so the entire colon is examined.

Second, the preparation to clean the colon beforehand is more rigorous and takes longer. Starting the day before the procedure, the patient drinks only clear liquids. Special laxatives are taken by mouth to clean all stool out of the colon.

Third, because the longer scope causes more pressure, patients receive sedating medication intravenously to prevent or reduce discomfort. Someone must drive the patient home after the procedure.

Fourth, compared with sigmoidoscopy, colonoscopy has a slightly higher risk of causing a tear or perforation in the colon. Perforation occurs in about one in 1,000 colonoscopies and the tear must be surgically repaired. Fortunately, perforation rates have fallen in recent years.

Like all medical tests, sigmoidoscopy and colonoscopy can give false negative results by missing small polyps. Fortunately, these tests rarely miss cancers or pre-cancerous polyps in the areas examined.

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What is the best screening test for colon cancer?

Studies show that colonoscopy is more accurate than annual fecal occult blood testing or sigmoidoscopy for detecting polyps and cancer because it examines the entire colon. Also, after a normal colonoscopy, patients at average risk of developing colon cancer usually need the test repeated only every 10 years. For these reasons, colonoscopy has become more popular for screening average risk patients. However, colonoscopy may not be the best choice for everyone. Some people find the bowel preparation and procedure cumbersome and time consuming. Others find the risk of perforation (though quite small) unacceptable.

Colonoscopy is always recommended for screening people at higher risk of colon cancer. Higher risk includes those with a family history of colon cancer or polyps with cancerous potential in a sibling, parent or child. Higher risk patients should begin screening earlier than average risk patients.

We recommend you discuss with your physician the age at which you should begin colon cancer screening, but screening should begin no later than 50 years of age.
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What about other tests?

"Virtual" colonoscopy, or computed tomography (CT) of the colon after bowel cleansing, is currently being studied in research centers, but in our view this screening test is not ready for widespread use.
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What does PAMF recommend?

Periodic screening for colon cancer in average risk patients should begin at 50 years of age.

PAMF recommends either:

1. Colonoscopy every 10 years or
2. Fecal occult blood testing every year, PLUS flexible sigmoidoscopy every five to 10 years for the average risk patient.

Remember: Appropriate screening can help prevent or cure colon cancer. We strongly recommend that you keep your colon cancer screening tests up to date.

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