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Janet Gray, Ph.D.
Janet Gray, Ph.D.

As author of our 2008 and 2010 State of the Evidence reports, Dr. Gray drives the science behind all our work.

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Agricultural Workers and Communities

Individuals who work or live in agricultural settings are likely to encounter elevated exposures to pesticides. Studies of agricultural workers and communities suggest that some of these exposures may be linked to elevated risk for breast cancer.

A case-control study of 128 Latina agricultural workers newly diagnosed with breast cancer in California identified three pesticides — chlordane, malathion and 2,4-D (2,4-Dichlorophenoxyacetic acid) - associated with an increased risk of the disease. Scientists found that the risks associated with use of these chemicals were higher in young women and in those with early-onset breast cancer than in unexposed women (Mills, 2005). These results are consistent with laboratory studies in which exposure to malathion led to increased proliferation of mammary cells as well as increased development of ductal mammary cancers. When rats were exposed concurrently to malathion and the natural estrogen estradiol, the incidence of both ductal and lobular types of mammary cancers increased (Calaf, 2011). 

Researchers from the National Cancer Institute studied the association between pesticide use and breast cancer risk in farmers’ wives in the Agricultural Health Study. This large prospective cohort study enrolled more than 30,000 women in Iowa and North Carolina. Researchers found evidence of increased incidence of breast cancer in women exposed to 2,4,5-TP (2,4,5-trichlorophenoxypropionic acid) and possibly in women exposed to another pesticide, dieldrin, as well as the fungicide ethanethiol (captan). However, the small number of cases among those who had personally used pesticides precluded firm conclusions. Incidence was also modestly elevated in women whose homes were closest to areas of pesticide application (Engel, 2005).

A 2007 study shows that young children of farmers using 2,4,5-TP on their crops had high levels of the pesticide in their urine samples soon after the chemical had been applied to the fields (Alexander, 2007). This is of concern, given the evidence of increased susceptibility of children and young adolescents to the carcinogenic effects of chemicals.