By Amy Norton

NEW YORK (Reuters Health) - Screening tumors from all colon cancer patients could be a cost-effective way of spotting families at high genetic risk of the disease, a study published Monday suggests.

Of the roughly 160,000 Americans diagnosed with colon cancer each year, about 3 percent have an inherited condition called Lynch syndrome, which involves abnormalities in particular genes that help repair damage to body cells' DNA.

Over time, that unchecked damage is likely to result in cancer: A person with Lynch syndrome has an 80 percent chance of developing colon cancer at some point -- often before the age of 50.

Lynch syndrome also carries higher-than-normal risks of developing tumors in the uterus (endometrial cancer) and several other organs, including the ovaries, stomach, liver and kidney.

Right now, families affected by Lynch syndrome are most often identified based on "clinical suspicion," said Dr. Uri Ladabaum, the lead researcher on the new study.

If a patient has, for example, multiple relatives who've had colon cancer, or a family member who developed the cancer at a young age, a doctor might suspect Lynch syndrome.

The problem with that approach is that it may miss many affected families, said Ladabaum, who directs the gastrointestinal cancer prevention program at Stanford University in California.

Another, more systematic option is to screen all colon cancer patients' tumors for signs of abnormalities linked to Lynch syndrome. If a tumor tests positive, patients can have the far pricier blood tests for detecting Lynch gene mutations, which confirm a diagnosis.

From there, close family members can be offered blood testing. If they, too, have Lynch syndrome, they can take steps to catch cancer early, or possibly prevent it.

Frequent colonoscopies can detect colon tumors early, for instance, or even prevent the disease by spotting pre-cancerous growths (called polyps) that are then removed.

Women may also opt to have their uterus and ovaries surgically removed, to eliminate the risk of endometrial and ovarian cancers.

According to the new study, published in the Annals of Internal Medicine, such steps could prolong mutation-carrying women's lives by up to four years on average.

Some U.S. medical centers are already screening tumors from all colon cancer patients, Ladabaum noted in an interview.

"And there is a growing consensus that this is a good idea," he said.

But whether the tactic is cost-effective is unknown.

So for their study, Ladabaum's team used a computer model to estimate the cost-effectiveness of different approaches to spotting families with Lynch syndrome.

One was to screen tumors from all colon cancer patients, then go from there. Another was to go directly to genetic blood tests for all patients. A third was to ask patients about their family history, and if suspicions were raised, either test their tumors or go straight to genetic blood tests.

It turned out that tumor testing first, followed by genetic tests if needed, was the most cost-effective. (A medical intervention is generally considered cost-effective if it rings in at $50,000 or less for every year of life gained.)