Lung cancer. Cancer of any location can happen to any person. Because cigarette smoke is rich with cancer-causing agents, people who smoke are much more susceptible to getting cancer at sites affected by smoke (mouth, throat, lungs). As less people smoke, at least in the us, we're seeing more cancers in non-smokers and at a younger age. In some lung cancers, they are people with a gene mutation called egfr.
Different causes. Non or never smokers can develop lung cancer if they have a genetic mutation to such genes as egfr or eml4/alk fusion translocation. Also, patients with high second hand smoke exposure may develop lung cancer as well. Radon exposure is the second leading cause of lung cancer in the United States.
We don't know. Although smoking is by far the greatest risk factor for lung cancer, not every lung cancer patient has a smoking history. Some non-smokers have other risks like second hand smoke or asbestos exposure. But a growing number have no risk factors that we know of. Unfortunately the lack if cigarette exposure does not completely rule out the possibility of lung cancer.