Causes
Smoking is the main risk factor for lung cancer and is responsible for more
than 80% of lung cancers. The longer you have smoked and the more you smoke,
the more likely you are to get lung cancer. If you stop smoking before a cancer
develops, lung tissue that has been damaged by smoking will start to repair.
An ex-smoker's risk will not be as low as that of a person who never smoked,
but over time, it will fall. Cigar smoking and pipe smoking are almost as
likely to cause lung cancer as cigarette smoking is.
Even second-hand smoke, the kind inhaled from nearby smokers, can cause lung
cancer. Non-smokers who are married to smokers have a 30% greater risk of developing
lung cancer than spouses of non-smokers. Recently, a woman who worked in a smoking
environment, but never actually smoked herself, developed lung cancer and was
able to claim it as a work-related injury.
Living in an environment with high air pollution or working with radioactive
minerals or asbestos can also increase the risk of cancer. Research has helped
us to understand how these risk factors produce certain changes in the DNA of
lung cells. These changes cause the cells to grow abnormally and form cancers.
DNA is the genetic material that carries the instructions for nearly everything
our cells do. Some genes (parts of our DNA) contain instructions for controlling
when cells grow and divide. The risk factors discussed earlier can trigger changes,
also called mutations, in these genes that result in cancer. A risk for
some types of cancer (e.g., breast, ovarian, colorectal, and several others)
can be inherited from parents. However, inherited gene mutations are not thought
to be a cause of very many lung cancers.