As we age, our cells acquire cancer-causing mutations, but mutations alone are rarely enough to start a tumor. An environmental trigger, such as exposure to air pollution from sources such as combustion engines, coal burning and cigarette smoke may be needed to tip mutant cells into cancer. Currently, lung cancer screening is offered only to people over a certain age who have previously smoked, missing never-smokers and individuals exposed to high levels of pollutants who may also be at risk of the disease.