THE IDENTIFIABLE CAUSES OF CANCER: TOBACCO
The question the reader will ask at this point is ‘Given all this epidemiological study, do we know the causes of cancer?’ Broadly the answer is ‘yes’ in many circumstances and for many cancers, and the opportunities for prevention that this understanding generates are there to be taken. We do not always know how the factors that have been identified by the epidemiological studies discussed in this chapter link up to what is being learned in the laboratories of the molecular biologists. This connection is being made rapidly and will be increasingly clear by the end of the century. Epidemiology has been very successful in discovering or confirming which features of our lives in the Western world can be now identified as causes of cancer.
Tobacco smoking has been shown to be the cause of most lung cancers in the Western world, particularly in men, but the link is becoming increasingly apparent in the developing countries. Probably 40 per cent of all cancer deaths in men and some 20 per cent in women are attributable to smoking, with the majority being caused by lung cancer, but with important and well-demonstrated links to cancers of the larynx, mouth, gullet and bladder, and with some suggestion also that there is a link to cancers of the kidney, cervix, nose and even the stomach. Tobacco sniffing and chewing also cause cancer, and smokers can quite possibly cause cancers in those who live with them by the process of passive smoke inhalation. Constituents of tobacco smoke can be found in the body fluids of non-smokers.