Sizing up a smoker's risk of lung cancer.

Black smokers run a greater risk of developing lung cancer than white smokers. Although the mechanism underlying that racial difference remains a mystery, scientists now suggest that black smokers may have a greater metabolic predisposition to the malignancy,

The new research may also provide more ammunition for those battling the tobacco industry. Many scientists believe that cigarette manufacturers aggressively target blacks in advertising campaigns designed to draw in new smokers.

John Richie Jr., a biochemist at the American Health Foundation in Valhalla, N.Y., and his colleagues knew that tobacco contains NNK, a nicotine-derived compound that causes lung cancer in mice. The team wanted to find out whether they could detect any differences in the way smokers metabolize this chemical.

They started their investigation by recruiting 25 white and 31 black smokers. The researchers analyzed urine samples from each smoker, homing in on two breakdown products of NNK: NNAL and NNAL-Gluc. NNAL also causes lung cancer in mice. When the body detoxifies NNAL, NNAL-Gluc results.

The researchers hypothesized that smokers whose bodies transformed NNAL into NNAL-Gluc more efficiently would face a reduced cancer risk. Their findings revealed that, on average, blacks in the study tended to detoxify NNAL less effectively than whites who smoked the same number of cigarettes.

The researchers speculate that many black smokers are less able than white smokers to detoxify NNAL.

Yet averages don't tell the whole story. The research showed that 6 percent of the black smokers detoxified NNAL aggressively and thus were at less risk of lung cancer than most other black smokers. By contrast, 30 percent of white smokers metabolized NNAL aggressively.

Additional metabolic differences may exist in the way blacks and whites handle the carcinogens in cigarette smoke. For example, compared with white smokers, black smokers run less risk of developing bladder cancer. If scientists can elucidate such differences, they may someday devise tests that give smokers individual portraits of their cancer risks.

"That information would be extremely useful in getting people to quit smoking," Richie says. "If you know you're at especially high risk for cancer, that might be all that much more incentive to give it up."

The researchers say that confirming the finding will require more research. "If it holds up, it's going to be very exciting, comments Steven Tannenbaum, a toxicologist at the Massachusetts Institute of Technology.

The question of whether an individual smoker gets lung cancer remains a highly complex one, Tannenbaum says. Some people may inherit a vulnerability to such cancers. However, many other factors go into the lung cancer and smoking equation, he adds.