Exposure to occupational carcinogens and social class differences in cancer occurrence.

It has been estimated that occupational exposures are responsible for about 4% of all human cancers in industrialized countries. These cancers are concentrated among manual workers and in the lower social classes, thus contributing to the social class gradient in cancer incidence and mortality. On the basis of the 1971 cancer mortality data from England and Wales, it was estimated that occupational cancer is responsible for about a third of the total cancer difference between high (I, II and III-NM) and low (III-M, IV and V) social classes, and for about half of the difference for lung and bladder cancer. However, direct evidence on the extent of the contribution of occupational exposure to carcinogens to social class differences is lacking, and several problems, such as the possible interaction between carcinogens and the effect of extraoccupational confounding factors, add further elements of uncertainty.