Causes

Like other cancers, lung cancer begins when the set of genetic instructions (the DNA) in certain cells becomes altered, or mutated, and the cells start growing out of control. Over the course of many years, one of these clusters of cells can become a tumor, and bits of the tumor may break off and travel throughout the body, producing new areas of cancer.

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Many different factors produce these initial genetic changes. Tobacco smoke, for instance, contains a host of cancer-causing chemicals. Still, some people who are not thought to have had significant exposure to these chemicals also develop lung cancer.