THE IDENTIFIABLE CAUSES OF CANCER

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. Sunlight. Ultraviolet irradiation from the sun is the main cause of skin cancers, including melanoma. Alcohol. Alcohol contributes to cancers of the upper digestive tract, particularly in combination with smoking. It probably also contributes to cancers of the liver, mainly, but perhaps not exclusively, through causing cirrhosis of the liver. There is little doubt that advice on the avoidance of heavy drinking is sound if we wish to reduce cancer risk as well as the other risks with which drinking is associated.Occupations. Cancer epidemiology really began with Percival Pott and his chimney-sweeps, and, for many researchers, creating a safe workplace and eliminating risks is a central purpose of epidemiological studies. Chemical dyes and asbestos have been identified as causes of cancer and eliminated in the workplace, but constant vigilance is still in order. New and stringent regulations permitting only limited exposure to substances hazardous to health arc now in force in many Western European countries, and their extension to Eastern Europe represents a significant financial, political and medical challenge.Environmental Pollution. Most of the factors that are hazardous in the workplace arc found in lower concentrations in the general environment and may well contribute to cancer risk. Atmospheric pollution probably plays only a limited role in lung cancer, but asbestos in the general environment has undoubtedly contributed to the level of risk.*33\194\4*

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