Smoking leads to lung cancer for some, while other smokers skate the disease. A new study presented at the American Association for Cancer Research annual meeting might offer an explanation, reports NPR.

A chemical that appears in the urine of smokers, NNAL, has been linked to lung cancer. New research suggests that lung cancer risk is elevated by 8.5 times in smokers with the greatest amount of the chemical, coupled with extraordinarily high nicotine levels.

Five hundred people in Shanghai and Singapore were studied.

"A history of smoking has always been thought of as a predictor of lung cancer, but it is actually not very accurate," Dr. Jian-Min Yuan, associate professor of public health at the University of Minnesota, told NPR. "Smoking absolutely increases your risk, but why it does so in some people but not others is a big question."

NNAL is produced when the body metabolizes tobacco. It is known to lead to lung cancer for test animals, but no one has ever tested its effects on people before this study. Genetics are thought to be the reason why some people's bodies make moreNNAL than others and, as a result, puts some people at a higher risk for lung cancer.            

Even if your body doesn't naturally produce a lot of NNAL, researchers still want to remind folks that smoking has other health risks, including heart disease, emphysema and other cancers.

However, people that do have more NNAL should be tested more often for lung cancer, said Tyler Jacks, the soon-to-be leader of the American Association for Cancer Research. Tyler, who is also a lung cancer researcher at MIT, said more frequent testing could lead to early detection and more options for patients.

The study took a decade to complete and included 246 smokers who developed lung cancer and 245 smokers who didn't get lung cancer.

A moderate amount of NNAL produced a 43 percent surge in risk for the cancer, while smokers with the highest levels saw their risk double, as compared to those with the least amount of NNAL.

Even after evaluating how much the people smoked, how long they had been smoking and the amount of cotinine (another chemical) found in the urine the risk levels remained the same.

-- Whitney Teal

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