Daily News Archive
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.