Environmental cancer risk factors. A review.

The risk of cancer in humans is increased by a wide spectrum of factors, which ranges from exposure to an identified agent, such as environmental chemicals or a virus, to a culturally determined behaviour, such as smoking, or to socio-economic conditions. We are today able to intervene on some of these factors, while others affect risk by as yet undetermined pathways. Only progress in the understanding of the mechanisms by which these factors act can lead to specific means of cancer prevention. There is no compelling reason to believe that the number of carcinogenic agents, to which humans can be exposed, is infinite, nor is it unreasonable to assume that it will eventually be possible to identify most of them. The variety of cancer risk factors of which we are presently aware implies, however, that it would be impossible to have just one simple approach to cancer control and cancer prevention. It is rather encouraging that the applicability of new laboratory methods to epidemiological surveys seems to open the way to a laboratory-integrated epidemiology.