The cause of the great majority of lung cancers is cigarette smoking. If several members of the same family have lung cancer the most likely reason is that they are all smokers. However, there is some evidence to suggest that lung cancer is more common in smokers in some families than smokers in the general population, but the reason for this is unclear. It is thought that some families may carry an increased susceptibility to the effects of smoking and therefore have an increased risk of lung cancer.

There is a study in the UK called GELCAPS (Genetic lung cancer predisposition study) which is trying to find out if there is a lung cancer gene. This involves taking blood samples from a person with lung cancer and their partner. It will be several years before the results of these studies are known. There is also some evidence to show that non smoking family members may have an increased risk of lung cancer from exposure to smoke from family members who smoke (passive smoking).

At the moment there is no evidence to suggest that lung cancer can be inherited (passed from one generation to the next) but there is strong evidence t that smoking and exposure to smoking are the main causes. Avoiding these risk factors will greatly reduce a person's chance of developing lung cancer.