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Pesticides Linked to Prostate Cancer
(May 2, 2003)
According to the National Cancer Institute, exposure to certain agricultural pesticides may be associated with an increased risk of prostate cancer among pesticide applicators, based on the findings of a large study looking at the causes of cancer and other diseases in the farming community. The study, part of a long-term study of pesticide applicators and their spouses known as the Agricultural Health Study (AHS), appears in the May 1, 2003, issue of the American Journal of Epidemiology. The AHS is a collaborative effort involving the National Cancer Institute (NCI), the National Institute of Environmental Health Sciences, and the Environmental Protection Agency.

The AHS report evaluated the role of 45 pesticides and found that a few of them showed evidence of a possible association with prostate cancer among pesticide applicators. Methyl bromide was linked to the risk of prostate cancer in the entire group, while exposure to six other pesticides was associated with an increased risk of prostate cancer among men with a family history of the disease.

"Associations between pesticide use and prostate cancer risk among the farm population have been seen in previous studies; farming is the most consistent occupational risk factor for prostate cancer," said Michael Alavanja, Dr.P.H., from NCI's Division of Cancer Epidemiology and Genetics in Bethesda, Md., and principal investigator of the AHS.

The current study included 55,332 men who are classified as either "private pesticide applicators" (92 percent) or "commercial pesticide applicators" (8 percent). Between 1993 and 1999, 566 new prostate cancers developed among all applicators, compared to 495 that were predicted from the incidence rates in the two states. This means that the risk of developing prostate cancer was 14 percent greater for the pesticide applicators compared to the general population. The men in this study were followed for about 4.3 years.

Methyl bromide is a fumigant gas used nationally to protect crops from pests in the soil and to fumigate grain bins and other agricultural storage areas. The scientists found that among both North Carolina and Iowa pesticide applicators, the risk of prostate cancer rose with increasing frequency of use of methyl bromide and with longer lifetime exposure to this pesticide. Elevated risks were seen at the two highest levels of exposure (out of five possible levels). Risks were two to four times higher than among men who were not exposed to methyl bromide. Based on animal studies, the National Institute for Occupational Safety and Health (NIOSH) lists methyl bromide as a potential occupational carcinogen.

The researchers found another link between pesticides and prostate cancer: among men with a family history of prostate cancer, exposure to six pesticides -- chlorpyrifos, coumaphos, fonofos, phorate, permethrin, and butylate -- was associated with an increased risk of prostate cancer. This effect was not seen among those without a family history. This type of finding, i.e., something appearing in only a subgroup of the entire study population, is particularly difficult to interpret, since it could result from chance or from differences between subgroups other than their use of pesticides. However, four of these pesticides, chlorpyrifos, coumaphos, fonofos, and phorate, are thiophosphates and share a common chemical structure. These findings suggest that certain pesticides may interact with a particular form of one or more genes shared by men with a family history of prostate cancer, making them more susceptible to developing the disease.

The most consistent risk factors associated with prostate cancer are age, family history, and African-American ethnicity. Hormonal factors and high levels of animal fat and red meat in the diet are also suspected risk factors. Several previous occupational studies have linked farming to prostate cancer risk. However, the variety of environmental exposures in the farming community such as pesticides, engine exhausts, solvents, dusts, animal viruses, fertilizers, fuels, and specific microbes, have made it difficult for researchers in previous studies to sort out which of these factors is linked to specific diseases.

For further information on the study, visit the AHS homepage: http://www.aghealth.org.

Coverage of this study was covered by a local Iowa Waterloo newsource again in March 2004.