Cigarette smoking is the most significant cause of lung cancer. Research as far back as the 1950s clearly established this relationship.
Cigarette smoke contains more than 4000 chemicals, many of which have been identified as causing cancer.
A person who smokes more than 1 pack of cigarettes per day has a risk of developing lung cancer 20-25 times greater than someone who has never smoked.
Once a person quits smoking, his or her risk for lung cancer gradually decreases. About 15 years after quitting, the risk for Lung Cancer decreases to the level of someone who never smoked.
Cigar and pipe smoking increases the risk of lung cancer but not as much as smoking cigarettes does.
About 85% of lung cancers occur in a smoker or former smoker. The risk of developing lung cancer is related to the following factors:
The number of cigarettes smoked
The age at which a person started smoking
How long a person has smoked (or had smoked before quitting)
Other causes of lung cancer include the following:
Passive smoking, or sidestream smoke, presents another risk for lung cancer. A person living with a smoker has twice the risk of lung cancer of someone not regularly exposed to smoke.
Air pollution from motor vehicles, factories, and other sources may increase the risk for lung cancer, but the degree of increase has not been established accurately.
Asbestos exposure increases the risk of lung cancer by 9 times. A combination of asbestos exposure and cigarette smoking compounds the risk by as much as 50 times.
Lung diseases, such as Tuberculosis (TB) and chronic obstructive pulmonary disease (COPD), also create a risk for lung cancer. A person with COPD has a 4-6 times greater risk of lung cancer even when the effect of cigarette smoking is excluded.
Radon exposure poses another risk.
Radon is a by-product of naturally occurring radium, which is a product of uranium.
Radon is present in indoor and outdoor air.
The risk for lung cancer increases with significant long-term exposure, although no one knows the exact risk.
Certain occupations where exposure to arsenic, chromium, nickel, aromatic hydrocarbons, and ethers occurs may increase the risk of lung cancer.
A person who has had lung cancer is more likely to develop a second lung cancer than the average person is to develop a first lung cancer.