Asbestos cancers as an example of the problem of comparative risks

Major differences in excess cancer risks have occurred in the asbestos industry in the past; part of this difference is probably related tp dustiness, part to the type of fibre used. In the case of mesotheliomas there is evidence of a major effect of the fibre type in the order of risk, crocidolite greater than amosite greater than chrysotile greater than anthophyllite. Differences of risk within an industry indicate that there is a dose response relation for both bronchial cancers and mesotheliomas. Also that in some instances it has been possible to identify lightly exposed groups in which no excess risks were detectable. As these least exposed groups are likely to have had several orders of magnitude heavier exposure than the general population, the risks to the general public are likely to be negligible. Bronchial cancers in absolute numbers are the major excess risk and are highly smoking-related. Stopping cigarette smoking is likely to be of paramount importance in reducing the excess cancer risks in asbestos-exposed individuals. Cancers in other sites which may possibly be related to asbestos exposure need further study even though the magnitude of the excess risk has been small compared to the lung cancers. In my view it is now possible to use the epidemiological evidence and experimental results to predict with fair confidence the physical and chemical characters and dose of natural and man-made fibres which will not cause a significant hazard in the future.