Gene ups oral-cancer risk for drinkers who smoke.

People who have a particular variant of a single gene are at a disproportionate risk of oral cancer if they both smoke and drink, researchers have found. The gene variant codes for a slow-acting form of alcohol dehydrogenase, an alcohol-metabolizing enzyme.

Oral cancer generally strikes long-term users of both alcohol and tobacco. It's relatively rare in the United States but is the third most prevalent form of cancer in the world.

In the new study, Edward Peters of the Harvard School of Public Health in Boston and his colleagues recruited about 1,200 Boston-area volunteers, half of whom had oral cancer. The researchers asked each volunteer about his or her smoking and drinking habits and took blood samples

to identify the form of enzyme each person carried.

Among volunteers with the slow-acting enzyme, those who reported consuming more than 30 drinks per week and having smoked sometime were 11 times as likely to contract oral cancer as light-drinking nonsmokers were. Smoking and heavy drinking also increased risk in people with the normal enzyme, but only by a factor of 6.

For nonsmokers who drank fewer than 30 drinks per week, the form of alcohol dehydrogenase had no bearing on oral cancer risk, Peters reported on March 30 at the meeting of the American Association for Cancer Research in Orlando.