Question

what is lung cancer and why it is caused

Answer 1

The incidence of lung cancer is strongly correlated with cigarette smoking, with about 90% of lung cancers arising as a result of tobacco use. The risk of lung cancer increases with the number of cigarettes smoked over time; doctors refer to this risk in terms of pack-years of smoking history (the number of packs of cigarettes smoked per day multiplied by the number of years smoked). For example, a person who has smoked two packs of cigarettes per day for 10 years has a 20 pack-year smoking history. While the risk of lung cancer is increased with even a 10 pack-year smoking history, those with 30 pack-year histories or more are considered to have the greatest risk for the development of lung cancer. Among those who smoke two or more packs of cigarettes per day, one in seven will die of lung cancer. But even though the risk is higher the more you smoke, there is no safe level of exposure to tobacco smoke.