AGRICULTURAL EXPOSURES AND CANCER TRENDS IN DEVELOPED-COUNTRIES

Recent increases have been reported in industrial countries for several sites of cancer. The causes of these increases remain unknown. Efforts should proceed to identify those occupational groups with increases in the same sites, as these may indicate relevant exposures. Two analyses were undertaken: trends in cancer mortality in industrial countries were reviewed to identify recently increasing sites and summaries were compiled of studies on farmers which have shown increased risks-for these same sites of cancer. Using data provided by the World Health Organization, age-specific rates were developed for a number of sites of cancer from 1968 to 1986. Trends in the ratio of male to female cancer mortality were also assessed for several of these countries. Based on a literature review by the National Cancer Institute, patterns of cancer in farmers reported in 20 studies from 8 countries are summarized, weighting each study by its size to create combined relative risks. In industrial countries, rates of cancer mortality increased for a number of sites, including melanoma, prostate, non-Hodgkin's lymphoma, multiple myeloma, breast, brain, and kidney cancer. The ratio of male to female cancer mortality (for all sites of cancer excluding lung) has generally increased in several countries during this same time period. Many of the same sites that have increased in the general population have also been found to be increasing in farmers. Significant excesses occurred for Hodgkin's disease, multiple myeloma, leukemia, skin melanomas, and cancers of the tip, stomach, and prostate. Nonsignificant increases in risk were also noted for non-Hodgkin's lymphoma and cancers of connective tissue and brain in many surveys. These excesses occurred against a background of substantial deficits among farmers for total mortality, heart disease. and many other specific diseases. Epidemiologic studies of farmers, and other occupational groups with excess rates of these same sites of cancer, may help to identify specific causal exposures that partly account for the rising trend of certain cancers in developed countries. Despite a number of common causes, heart disease and some sites of cancer show opposite trends in the general population, with the former decreasing and the latter increasing. Thus, the causes of the increases in cancer are not likely to stem from those that are shared with heart disease, but to represent some as-yet-unrecognized risk factors. Among those that should be carefully reviewed are solvents, pesticides, engine exhausts, and animal viruses, materials to which both farmers and the general population are exposed in increasing amounts.