Colorectal Cancer Genetics
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By Kate Travis

Colorectal Cancer Genetics

A set of traits predicts Lynch syndrome

By Kate Travis


Researchers have developed a simple model that may help identify cancer patients who, along with their families, should be tested for a genetic condition called Lynch syndrome. People with the inherited condition should have increased cancer screenings because they’re at high risk of colorectal and other cancers, especially at young ages.

Lynch syndrome, also called hereditary nonpolyposis colorectal cancer, is expected to cause 3 percent to 5 percent of 150,000 new cases of colorectal cancer in the U.S. this year. Researchers estimate that those with the syndrome have as much as an 80 percent chance of developing colorectal cancer during their lifetimes.

People with Lynch syndrome have mutations in DNA mismatch repair genes, which act as a sort of spell checker for a person’s DNA, explains cancer researcher Asad Umar of the National Cancer Institute. “If one of the genes in the DNA mismatch repair pathway is mutated, it makes the spell checker malfunction,” Umar says.

Researchers in Edinburgh, Scotland, identified 870 people younger than 55 who were diagnosed with colorectal cancer between 1999 and 2003 in Scotland; 4 percent had Lynch syndrome. The researchers found that traits such as sex, age, tumor location, number of tumors, and the age of relatives with colorectal or endometrial cancer could help identify which patients have Lynch syndrome.

They used this information to develop a model that predicts a patient’s likelihood of having Lynch syndrome. It may help doctors decide whether further testing for the syndrome, including expensive genetic testing, is appropriate.

If testing indicates a patient has Lynch syndrome, “we can then offer other family members genetic testing,” says clinical geneticist Mary Porteous of the South East of Scotland Genetic Service. Family members with a mutation should have enhanced cancer screening, says Porteous, a co-author of the study, which was published in the June 29 New England Journal of Medicine.

The researchers tested their model’s validity in 155 additional colorectal cancer patients. Because this is a small number of patients, they caution that the model isn’t yet ready for wide use.

People who are at high risk for cancer mutations should be aware of the risks and benefits of genetic testing, notes Nancy Roach, president of the advocacy organization C3: Colorectal Cancer Coalition. “Working with an experienced genetic counselor is critical.”

The take-home message from the new study, Porteous says, is to discuss family history of disease: “The more open people can be, the better it is for trying to provide optimal care for the rest of the family.”  CR endbox