They said people with high concentrations in their urine of a nicotine byproduct called NNAL had double the risk of developing lung cancer compared to smokers with lower NNAL concentrations in their urine.And smokers who had high urine levels of both NNAL and another nicotine byproduct called cotinine had more than eight times the risk of lung cancer compared to smokers with the lowest concentrations of these two compounds.The findings may help explain why some smokers get cancer while others do not, they said."Smoking leads to lung cancer, but there are about 60 possible carcinogens in tobacco smoke, and the more accurately we can identify the culprit, the better we will become at predicting risk," said Jian-Min Yuan of the University of Minnesota, who presented the findings at the American Association for Cancer Research in Denver.Only about one in 10 smokers gets lung cancer.