Smoking is the leading cause of lung cancer, but how is it that so many smokers never develop the deadly disease? A collection of reports in the U.S. and Europe may have found an answer in the genes. Researchers identified two gene variants in 34% of the population that code for cell-surface proteins that in turn bind to nicotine molecules. Clamp nicotine to the cell this way, and dramatic changes can result, including amplified growth of blood vessels in the lungs, which can create an environment particularly well suited to greedy cancer cells. The studies determined that smokers who had one of the gene variants were 28% more likely than other smokers to develop lung cancer, and those with both had a staggering 81% higher risk. What's more, researchers found that smokers who have either of the gene variants may have a greater tendency toward nicotine addiction and are likely to smoke more often during the course of a day.