Effect of cigarette smoking on susceptibility to lung cancer.

Fisher first suggested that genetic predisposition to lung cancer is a more important factor than cigarette smoking, and that therefore one may smoke. Recently, this thesis has been defended strongly by Burch. Here, a literature survey has been done that indicates that the genetic susceptibility for development of lung cancer varies between individuals. But it is wrong to conclude from this that therefore one may smoke. Such a conclusion only would be valid, if there was a close relationship between the genetic tendency to smoke cigarettes, and the genetic tendency to develop lung cancer. The evidence that such a relationship does not exist is overwhelming. It is, therefore, valid to conclude that the large excess of deaths from lung cancer in cigarette smokers as compared to nonsmokers is a direct consequence of smoking cigarettes. To illustrate the effect of cigarette smoking on susceptibility to lung cancer, the distribution of susceptibilities to lung cancer in cigarette smokers and in nonsmokers has been derived. The shape of the susceptibility distribution is determined by the effects of all environmental carcinogens (both known and unknown) to which the population has been exposed, as well as by differences in genetic susceptibility between members of the population. The method described has general application.