How is it that a lot of nonsmokers get lung cancer?

Couple reasons. ..: Many have had significant "passive" exposure to tobacco smoke, either by a spouse or at work. Occassionally we can implicate a long-term exposure to an inhaled substance like fossil fuels. However, some people simply have a defect, or more likely, a couple of defects in their genetic code. These mutations can make cells in the lung divide without any way to control them, leading to cancer.

Less than smokers: There are still risk factors, genetic factors, exposure factors that lead to a variety of cancers.

See below: 15% of all lung cancers occur in never smokers. Epidemiological studies suggest that environmental toxic exposures (radon, second hand smoke, pollution etc) can be linked; however, for a given individual it is hard to establish a definite link; the biology of lc in never smokers is different and there are certain molecular features that may make it more responsive to certain drugs;.