The Causes of Lung Cancer
Youk'n hide de fier, but w'at you gwine do wid de smoke?
JOEL CHANDLER HARRIS
IT WILL HAVE become clear to the reader that even if cigarette smoking is responsible for lung cancer to some extent, it is neither a necessary nor a sufficient cause for that or any other disease. Ten per cent of lung cancer cases occur among non- smokers; this proves that smoking is not necessary in order to have people die from lung cancer. Similarly, it has been found that one in every eleven men aged 25 who smoked more than 25 cigarettes a day will die of lung cancer before attaining the age of 75; that means that 10 out of II who smoked this quite large number of cigarettes would survive without lung cancer. For those smoking between 15 and 25 cigarettes a day I man in 20 died of lung cancer; this leaves 19 out of 20 smoking moderately who would not at any time contract lung cancer. Thus cigarette smoking is not a sufficient cause of lung cancer either; the majority of those who smoke even in excess are not liable to die of the disease. These undisputed facts are seldom stated in quite this way, but I think it useful and valuable to be clear on this point.
It is precisely because smoking at most is neither a necessary nor a sufficient cause that it is so difficult to prove that is is a cause at all. In using the term 'cause' here we have, of course, to fall foul of modern philosophical discussions which have brought the whole concept of causation into some disrepute. The term is being used entirely in its common sense meaning