Among all cancers, lung cancer results in the most deaths each year. In fact, mortality from the disease exceeds the mortality of colon, breast, and other types of common cancers combined. The cancer originates in lung cells that mutate and begin to behave abnormally by excessively replicating. These cells form masses called tumors that eventually disperse cancer cells to other parts of the body.
The primary risk factor for lung cancer is cigarette smoking. Smoking damages lung cells over time, and although the body attempts to repair the damage, it sometimes results in mutations that lead to cancer. People can reduce their risk of developing cancer by never smoking or quitting.