Genetic Test Showing Increased CRC Risk Prompts No Action

Jenni Laidman

October 21, 2014

Genetic testing designed to determine the risk of developing colorectal cancer (CRC) failed to prompt people to sign up for CRC screening, even when the test showed an elevated risk of colon cancer, according to a study published online October 20 in the Annals of Internal Medicine.

The researchers suggest that their findings debunk a common claim in the media that enhanced information about individual genetic makeup will promote healthier behavior.

"It was a surprise," said lead investigator David S. Weinberg, MD, chair of internal medicine and chief of the gastroenterology section at the Fox Chase Cancer Center and Jefferson Medical College in Philadelphia.

Study participants who underwent folate testing combined with genetic screening were no more likely to follow-up with CRC screening than those who received no individual risk profile. "You would think that information about yourself that is so personalized — your own genes, your own level of folate — might be more effective in altering your behavior than being told about risk in the abstract," he told Medscape Medical News.

The study involved 783 people, 50 to 79 years of age, who were at average risk for CRC but had not been adherent to CRC screening recommendations, either fecal occult blood testing or colonoscopy.

These patients were assigned to receive either usual care or genetic testing plus environment risk assessment (GERA).

The environmental risk-assessment portion of the GERA looked at serum folate levels, and the genetic testing evaluated certain polymorphisms of methylenetetrahydrofolate reductase (MTHFR), a regulator of cellular folate metabolism. In combination with low serum folate, certain MTHFR polymorphisms can as much as double the risk for CRC.

In the subsequent 6 months, the rate of CRC screening between the usual care and GERA groups was not significantly different (35.7% vs 33.1%).

Surprisingly, in the GERA group, more people determined to be at average risk than at elevated risk followed-up with CRC screening (38.1% vs 27.9%; odds ratio [OR], 0.75), but the difference was not statistically significant.

The likelihood of undergoing CRC screening failed to reach significance even after adjustment for covariates such as age, sex, race, marital status, education, and multivitamin use.

"Everybody sort of assumed genetic testing would change the way people behaved," Dr. Weinberg said. "We came along and said, 'We are measuring your risk for a common disease before you have it, where we can tell you something and you can do something in the here-and-now to reduce that risk.' There is a widely agreed-upon risk-reduction strategy, but nobody did it."

Dr. Weinberg speculated that a degree of "genetic determinism" might have taken hold in the face of a test that showed an elevated CRC risk. "It becomes fait accompli. I'm going to get this disease, so why bother?"

Furthermore, Dr. Weinberg said, participants might not have understood, despite efforts to inform them, that CRC screening would be the correct next step. Another possibility is that the people didn't distinguish between genetic testing, which can determine risk but not diagnose disease, and screening tests, which can find precancerous and cancerous tissue.

This isn't the first study to show a disconnect between genetic testing and individual behavior. A previous study looked at 2037 individuals who underwent genetic testing (N Engl J Med. 2011;364:524-534). In the 6 months after testing, there were no changes in dietary fat intake, exercise levels, or symptoms of anxiety.

This research was paid for by the National Institutes of Health. Coauthor Eric Ross, ScM, from the Fox Chase Cancer Center, reports serving as a statistical consultant for the Annals of Internal Medicine.

Ann Intern Med. Published online October 20, 2014. Abstract

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