Who is at Risk for Lung Cancer?
The major risk factor for lung cancer is smoking. Harmful substances, called
carcinogens, in tobacco damage the cells in the lungs. Over time, the damaged
cells may become cancerous. The likelihood that a smoker will develop lung
cancer is affected by the age at which smoking began, how long the person
has smoked, the number of cigarettes smoked per day and how deeply the smoker
inhales. 
The more years you smoke and the more packs of cigarettes you smoke, the
higher your risk. Stopping smoking reduces a person's risk for developing
lung cancer. Physicians define a high-risk smoker as someone who has at
least “20-pack-years” of smoking history. This would
equate to one pack per day for 20 years, two packs a day for 10 years, etc.
Nonsmokers who breathe in the smoke of others, also called second-hand
smoke, also show increased risk for lung cancer.
Exposure to asbestos fibers is an important risk factor. Asbestos is a
group of minerals that occur naturally as fibers and are used in certain
industries. When asbestos particles are inhaled, they can lodge in the lungs,
damaging cells and increasing the risk for lung cancer. The risk of lung
cancer is even higher among asbestos workers who also smoke. Asbestos workers
should use the protective equipment and follow recommended work practices
and safety procedures.
Radon is an invisible, odorless and tasteless radioactive gas that occurs
naturally in soil and rocks. It can cause damage to the lungs that may lead
to lung cancer. High radon levels in some mines also can increase the lung
cancer risk for miners.