Milwaukee, Wis. ? For the first time, a simple blood test shows promise in helping predict the average person’s risk of developing the most common form of colon cancer.

Other blood tests either detect cancer after it has developed or identify the risk in people with rarer genetic or inherited forms of the disease.

The new blood test needs more study and won’t be available for at least several years. But it could become a screening tool that might someday make scope exams less frequent or sort out who needs them most and who can safely skip them.

“You might be able to spare people increased surveillance. It’s very unpleasant to get a colonoscopy,” said Andrew Feinberg, a Johns Hopkins University doctor who led the study published today in the journal Science.

The new blood test looks for a genetic switch that’s involved in other cancers, especially breast and ovarian, so it may hold promise for assessing the risk of those, too.