A new web-based tool may help people decide if they should seek genetic testing for an inherited form of colon cancer.

Lynch syndrome is rare, but is the most common hereditary form of colorectal cancer in the West, accounting for two to five per cent of all cases of the disease.

Researchers are developing tools to guide doctors and patients who are considering getting tested, as well as treatment and prevention options.

In one study, Dr. Sapna Syngal of the Dana-Farber/Brigham and Women's Cancer Center in Boston and her colleagues created a web-based questionnaire called PREMM1,2 for personal and family history, and tested its accuracy for Lynch syndrome.

"You get the patient and their doctor to fill out a series of questions that are pretty straightforward and then get a number that tells them, 'Well, do you have a high likelihood of carrying a mutation or don't you?'" said Syngal.

The researchers hope the model will make it easier for people to tell if they are at high risk.

The test was based on 898 people with a personal or family history pointing to Lynch syndrome.

Of the people who were referred to genetic testing for the two gene mutations linked to the syndrome, 14 per cent had either of the mutations. When the test was given to more than 1,000 people with the syndrome, about 15 per cent had the mutations, the researchers found.

Tests a work in progress

Researchers at Johns Hopkins University in Baltimore developed a second model, called MMRpro, that estimates probability based on family history of colorectal and endometrial cancer.

The results showed higher accuracy than existing alternatives and current clinical guidelines, Sining Chen and colleagues reported.

But genetic screenings are not foolproof, and cost about $3,000 US a test. The MMRpro also requires a lot of data to be entered.

Nonetheless, in an editorial accompanying both studies, Dr. James Ford and Alice Whittemore of Stanford University said the prediction rules should be useful to clinicians and their patients, as well as epidemiologists assessing the magnitude of the cancer and potential usefulness of preventive approaches.

For example, colonoscopies may prevent cancer by detecting tumours that are benign, before they become cancerous.

Several of the study authors reported ties to the lab conducting the genetic tests.