PhotoColorectal cancer, also known as colon cancer, is caused by tumors growing in parts of the large intestine. In the past a colon cancer diagnosis was very often fatal. By the time it was discovered, it was usually too late.

But since these tumors almost always start out as benign polyps growing in the large intestine, doctors believed they could drastically reduce colon cancer deaths if they could just discover – and remove – these polyps before they transformed into cancerous tumors.

Thus was born the colonoscopy, a procedure by which a tiny camera is inserted through the patient's rectum for a look around the large intestine. The probe is equipped with a surgical instrument that can remove most polyps that are discovered.

With this screening tool, doctors expressed confidence they could significantly reduce the rate of colon cancer. But first, patients had to agree to submit to a colonoscopy and the public, it turned out, was a bit squeamish about this rather invasive procedure. Having to drink the unpleasant colon-cleansing cocktail the night before didn't help.

The Couric effect

Then there seemed to be a rather abrupt shift in the public attitude. In March 2000 NBC Today Show host Katie Couric underwent a very public colonoscopy on network television. Couric had become a strong advocate of the procedure after her husband Jay died of colon cancer.

Suddenly, more people were making appointments for colonoscopies, a result of what many doctors call “the Couric effect.” A later Archives of Internal Medicine study documented a 20% spike in colonoscopies in the wake of her broadcast.

For her part, Couric remains a strong advocate of the colonoscopy and, when it was time for her next one, once again invited the cameras in, resulting in a video that is both humorous and serious.

The American Cancer Society estimates there will be more than 102,000 new cases of colon cancer in the U.S. in 2013. At the same time, the group notes the death rate from the disease has been dropping over the last 20 years.

“There are a number of likely reasons for this,” the group says. One is that polyps are being found by screening and removed before they can develop into cancers. Screening is also allowing more colorectal cancers to be found earlier when the disease is easier to cure.

New evidence

A new study from the Harvard School of Public Health (HSPH) maintains 40% of all colorectal cancers could be prevented if people of average risk underwent a colonoscopy every 10 years. 

"Colonoscopy is the most commonly used screening test in the U.S. but there was insufficient evidence on how much it reduces the risk of proximal colon cancer and how often people should undergo the procedure," said Shuji Ogino, co-senior author and associate professor in the Department of Epidemiology at HSPH. "Our study provides strong evidence that colonoscopy is an effective technique for preventing cancers of both distal and proximal regions of the colorectum, while sigmoidoscopy alone is insufficient for preventing proximal cancer."

The study also found that people who get a clean bill of health after a colonoscopy have a significantly reduced risk of colorectal cancer for up to 15 years after the procedure, although the data support repeat screening at shorter intervals among individuals with a personal history of adenoma -- a benign tumor of glandular origin that can become malignant over time -- or a family history of colorectal cancer.

When to get one

Unless you happen to be 50 years old or older, you may not have to worry about a colonoscopy for a while. It's generally recommended that people of average risk undergo their first procedure at age 50 and then, assuming no polyps are found, follow up with another 10 years later.

Who is at risk for colon cancer? According to the Mayo Clinic, age is the greatest risk factor. The majority of people diagnosed with colon cancer are over age 50. African-Americans have a greater risk than other races and you might be more likely to develop the disease if you have a parent, sibling or child with the disease. If more than one family member has colon cancer or rectal cancer, your risk is even greater. 

There is some research suggesting colon cancer and rectal cancer may be associated with a diet low in fiber and high in fat and calories. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat.  

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