Cancer risks associated with agriculture: epidemiologic evidence.

Despite their generally favorable mortality experience, general occupational surveys of farmers suggest they have elevated risks of cancer of the lymphatic and hematopoietic systems, stomach, prostate, brain, and skin. Since farmers often serve in the role of mechanic, carpenter, welder, pesticide applicator, and veterinarian, they may be exposed to many potentially hazardous substances. The types and levels of exposures have been discussed by others earlier in the program. The evidence is strongest for the association between farming and risk of leukemia. However, the specific leukemogenic agent or agents have yet to be identified. Leukemia excesses among poultrymen and dairy farmers suggest involvement of zoonotic viruses, while associations with crop production is more indicative of pesticide usage. The associations regarding other cancers (i.e., Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma, soft-tissue sarcoma, and cancers of the stomach, brain, and prostate) are even less clear. However, the Swedish reports of high risk of soft-tissue sarcomas and lymphomas among persons exposed to herbicides is particularly disconcerting and underscores the urgent need for similar epidemiologic studies in the U.S. Several case-control interview studies are underway that should help clarify the role of agricultural factors in the origin of various cancers. NCI is sponsoring studies of leukemia and non-Hodgkin's lymphoma among men from Minnesota and Iowa. Detailed information on farm practices and pesticide usage is being gathered. A study of soft-tissue sarcoma, Hodgkin's disease, and non-hodgkin's lymphoma also has just been initiated. This investigation is located in Kansas, a major wheat producing area. A wheat producing area was selected because herbicides are more heavily used on this crop than insecticides. The major objective of this project is to evaluate the role of herbicides in the origin of these cancers. A case-control study of brain cancer has also recently been initiated. Although this study focuses on contact with petrochemicals, a complete work history will be obtained and would note any farm experience. These data may help clarify the reported association between brain cancer and farming.