People With Diabetes May Need Earlier Colon Screen

40-Somethings With Diabetes Have About the Same Risk of Precancerous Growths as 50-Somethings Without Diabetes

By Charlene Laino
WebMD Health News

Reviewed by Laura J. Martin, MD

May 22, 2012 -- Should people with diabetes be screened for colon cancer at younger ages than is usually recommended?

That may very well be the case, say researchers who found that people in their 40s with type 2 diabetes are about as likely to have precancerous colon growths called adenomas as people in their 50s without diabetes.

"It's almost as is if having diabetes advances your age by 10 years in this regard," says researcher Susan Hongha Vu, MD, a clinical gastroenterology fellow at Washington University School of Medicine in St. Louis.

If the findings are confirmed in a larger, more robust study, the guidelines should be changed so that people with diabetes start colon cancer screening at age 40, she tells WebMD.

Vu presented the study at the Digestive Disease Week conference in San Diego.

Colon Cancer Screening Guidelines

Current guidelines call for men and women at average risk to undergo regular colon cancer screenings beginning at age 50. Colonoscopy, which allows the doctor to view the entire colon and remove any abnormal growths, is the gold standard. There are several other screening options, though, such as flexible sigmoidoscopy and fecal occult blood tests.

But people at high risk of colon cancer should begin screening earlier, according to the recommendations.

Research suggests diabetes may be another such risk factor, Vu says.

"A lot of studies have shown an association between type 2 diabetes and an increased risk of colon cancer," she says.

"Studies also show that diabetes increases the risk of precancerous lesions in the colon," Vu says.

"But as far as we know, no one had taken the next logical step -- that is, to determine whether people with type 2 diabetes should be screened earlier," she says.

Study: Diabetes Appears to Affect Polyp Risk

So the researchers examined the medical records of three groups of people having a colonoscopy over a six-year period at their institution: 125 people ages 40-49 with type 2 diabetes, 125 people 40-49 without diabetes, and 125 people ages 50-59 without diabetes.

Colonoscopy found at least one precancerous polyp in:

  • 14% of those ages 40-49 without diabetes
  • 30% of those ages 40-49 with diabetes
  • 32% of those ages 50-59 without diabetes

Still, the study does not prove that diabetes causes or directly contributes to polyp growth.

People with diabetes may have other risk factors for adenomas and colon cancer that weren't measured, says John Petrini, MD, a gastroenterologist at the Sansum Clinic in Santa Barbara, Calif.

Vu says there is a possible explanation for a link between diabetes and colon cancer. People with diabetes have abnormally high levels of insulin in their blood, and insulin can fuel the growth of cells, including precancerous and cancer cells, she says.

The findings are intriguing, Petrini says. But until there is a large, well-designed study confirming the finding, it's too early to talk about changing guidelines, he says.

But should people with diabetes in their 40s go in for early screening if they are concerned? They could, Petrini says. But without guidelines, insurers are unlikely to cover the cost of the test -- about $1,000 in the case of colonoscopy, he says.

On the other hand, a person might opt for a less expensive flexible sigmoidoscopy, which is a good way of identifying people who need a full colonoscopy, Petrini says.

About 25 million Americans have diabetes, and that number is expected to double in the next 25 years. Over 1.1 million have colorectal cancer, according to the American Cancer Society.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

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SOURCES: Digestive Disease Week, San Diego, May 19-22, 2012. Susan Hongha Vu, MD, clinical gastroenterology fellow, Washington University School of Medicine, St. Louis. John Petrini, MD, gastroenterologist, Sansum Clinic, Santa Barbara, Calif.

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