Researchers suspect genetic susceptibility combined with exposure to cancer-causing substances like asbestos, radon ( a radioactive gas), certain solvents and other people`s tobacco smoke as probable causes.
The study conducted in Europe, North America and Asia, is based on 2.4 million non-smokers who had lung cancer .Male non-smokers are more likely to than female non-smokers to die of the diseases, the study found, and the overall risk to non-smoker are increasing.
Dr. Michael J. Thun, head of epidemiologic research for the America Cancer Society, who led the study said smokers are still much worse off. A man who has never smoked has a 1.1 in 100 risk of dying from lung cancer but the risk jumps to one in five if he smokes. In women, the risk goes from 0.8 in 100 to one in eight.
A trouble finding is the relatively high rates of lung cancer among non-smoking women in parts of Pacific Rim Countries. "one hypothesis is that the cooking fumes given off by woks contain all kind of carcinogens ," Dr. Thun said, adding that a likely culprit was cooking oil which vaporizes a high temperature
"The New York Times"