Even if everyone in the U.S. stopped smoking tomorrow, lung cancer would still be the third-leading cause of cancer death, the New York Times reported March 21.

The recent death of non-smoker Dana Reeve, 44, widow of actor Christopher Reeve, helped raise public awareness that smoking is not the sole cause of lung cancer. 

"Lung cancer is so closely linked up with smoking that doctors and the public are surprised when it turns up in nonsmokers," said Dr. Peter B. Bach, a pulmonologist and epidemiologist at the Memorial Sloan-Kettering Cancer Center in New York. "But they shouldn't be surprised. There are about 180,000 cases of lung cancer a year and 150,000 deaths. If 80 percent or so stem from smoking, that leaves about 36,000 cases and 30,000 deaths a year that are not related to smoking."

Besides smoking, causes of lung cancer include secondhand smoke, asbestos exposure, indoor radon, workplace carcinogens like vinyl chloride and diesel exhaust, scarred or irradiated lungs, air pollution, poor diet, and genetics.

In some ways, nonsmokers may be particularly vulnerable to dying from cancer because they elude early detection -- the best chance for surviving the disease. Simply put, neither patient or doctor are on the lookout for the disease among non-smokers.