Feasibility of monitoring populations to detect environmental carcinogens.
In relation to cancer, monitoring, i.e. "continuing observation in order to decide when changes in incidence or mortality may have occurred" can be of two types: (a) passive (or routine) monitoring using routinely collected cancer statistics for populations in general (b) active (or exposure-oriented) monitoring in which the cancer experience of groups with specific exposures is compared with that of the non-exposed. The advantages and disadvantages of mortality and morbidity data for passive monitoring are listed. It is concluded that passive monitoring can rarely do more than indicate areas for further study. The potential of active monitoring is examined by consideration of industrial and occupational exposures, the follow-up of persons on prolonged drug therapy (including transplacental effects) and changes in cancer risk following migration. As such studies are often univariate, it may not be possible to allow for the effect of other factors, and confirmatory studies will often be required. It is belived that priority should currently be given to monitoring occupational exposures, particularly those involving chemicals shown by animals studies to have carcinogenic activity. To monitor everybody for everything will result in nothing. The social responsibilities which devolve on monitors, the authorities, both sides of industry and the general public as a result of the establishment of monitoring systems are discussed. It is concluded that monitoring, active or passive, does not represent a quick road to the identification of environmental carcinogens but can point to products or processes likely to have a cancer risk - a risk which would have to be confirmed or otherwise by other methods.