17
Jun
More Data Links Endocrine-Disrupting Pesticides to Increase in U.S. Breast Cancer
(Beyond Pesticides, June 17, 2026) A study out of Michigan State University reviews robust county-level data on pesticide use and breast cancer incidence rates, determining that there are “modest positive associations” in rural counties in the United States. The findings were published in Cancer Causes & Control.
Public health and environmental advocates cite the proliferation of published, peer-reviewed research, like this new study, in support of a societal imperative to eliminate harmful agrichemicals and transition to organic practices. The U.S. and countries worldwide have standards for certified organic production, similar to the U.S. Organic Foods Production Act, that establish required practices, a national list of allowed and prohibited substances, public oversight and a stakeholder board with authority over allowed inputs, certification and inspection of on-farm practices, and an enforcement system to ensure standards compliance. There is limited federal investment in growing the organic sector, despite its productivity, profitability, and protection of healthy ecosystems. The study adds to the body of science that illustrates dramatic deficiencies in the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) under which the U.S. Environmental Protection Agency (EPA) and other federal statutes fall short in addressing the complex exposure patterns and adverse human and environmental effects, while allowing widespread harmful pesticide uses, including those that are currently banned in the European Union, Brazil, Japan, among others.
Methodology and Main Findings
The study included 2,457 counties after excluding counties with missing pesticide (77 counties) or breast cancer incidence data (609 counties, including entire states such as Minnesota, Virginia, Kansas, and Nevada). Researchers used data from the U.S. Geological Survey (USGS) Pesticide National Synthesis Project, which estimates county-level use of agricultural pesticides in kilograms. Cumulative average use data between 2001 and 2015 were used, covering 38 pesticides grouped into eight chemical classes: carbamates, neonicotinoids, organochlorines, organophosphates, phosphonates, pyrethroids, triazines, and miscellaneous:
- Carbamates: Aldicarb, Carbaryl, Lindane, and Propoxur.
- Neonicotinoids: Acetamiprid, Clothianidin, Dinotefuran, Imidacloprid, Thiacloprid, and Thiamethoxam.
- Organochlorines: Dicofol, Endosulfan, and Methoxychlor.
- Organophosphates: Azinphos-Methyl, Bensulide, Chlorpyrifos, Diazinon, Dicrotophos, Dimethoate, Disulfoton, Ethoprophos, Fenamiphos, Malathion, Naled, and Parathion Phorate.
- Phosphonates: Glufosinate and Glyphosate.
- Pyrethroids: Cypermethrin, Fenpropathrin, and Permethrin.
- Triazines: Atrazine, Propazine, and Simazine.
- Miscellaneous: Fosetyl, Terbufos, Tribufos, and Triclopyr.
While facing unprecedented cuts and elimination of core functions, the USGS website states that the agency will publish annual pesticide-use estimates for “approximately 400 compounds, from 2018-2022″ sometime this year. This is a significant expansion of their previous tracking of just 72 compounds as of 2019, which would allow for an expansion of the critical research conducted in the study.
Data for breast cancer incidence rates were gathered through the National Cancer Institute’s State Cancer Profiles between 2016 and 2020. A latency period of 5-15 years was built between pesticide exposure data (2001-2015) and the health outcome (in this case, cancer) window (2016-200) in order for the findings to be consistent with prevailing epidemiologic evidence. Counties are classified into rural or urban based on U.S. Department of Agriculture Rural-Urban Continuum Codes. The methodology, which can be found in more detail on pages 2-4 of the study PDF, considered confounding variables such as smoking, unemployment, residential mobility, poverty level, and education status.
The main findings for this study include:
- Rural Counties Disproportionately Impacted. Rural counties have a statistically significant relationship between higher breast cancer incidence rates and endocrine-disrupting pesticide exposure. The adjusted rate ratio (aRR), or a comparison of breast cancer incidence rates in counties with higher versus lower pesticide use after adjustments for confounding variables, was 1.02. In other words, there is a 2 percent higher breast cancer incidence rate in rural counties based on the 38 pesticides highlighted in this study.
- Neonicotinoids and Phosphonates. These two classes of pesticides, the latter of which includes glyphosate and glufosinate, show a specific significant positive association with higher rates of breast cancer after adjusting for confounding variables.
- Individual Pesticide-Level Analysis. Thiamethoxam (neonicotinoid) and chlorpyrifos (organophosphate) show a statistically significant relationship with higher rates of breast cancer.
- Higher Pesticide Use, Higher Breast Cancer Risk. In rural counties, the highest use of pesticides had meaningfully higher breast cancer incidence relative to the counties with the lowest documented pesticide use. The authors refer to the top third of highest pesticide counties as the top tertile, where tertiles are used to break data into three sets. The aRR for the highest tertile is 1.06, meaning there was a six percent higher breast cancer incidence in counties with the most annual pesticide use estimates.
- Pesticide Use Trends. Neonicotinoids, phosphonates, and pyrethroids are increasingly used between 2001 and 2015, whereas carbamates, organochlorines, organophosphates, triazines, and the selected miscellaneous pesticides are generally decreasing in use.
Previous Coverage
There are numerous investigations into the connection between pesticide use and exposure and breast cancer, as documented in the peer-reviewed literature.
Published in PLOS ONE, research in Brazil “analyzed the impact of occupational/ household chronic exposure to pesticides on the clinicopathological profile of breast cancer in rural women from Paraná southwest, a predominantly rural landscape with large pesticide uses,” finding that “pesticide exposure favors the occurrence of more aggressive breast cancer.” The women in the exposed group “reported spending at least 50% of their lives working with pesticides and having direct contact with these substances at least once a week,” with activities such as washing items contaminated with pesticides, preparing and diluting concentrated pesticides, and spraying diluted pesticides on crops. “Furthermore, 94% of the women in the exposed group reported performing these tasks without using PPE [personal protective equipment], not even gloves,” the researchers say. Among other findings, exposed patients have a higher prevalence (32.83%) of the more aggressive Luminal B subtype of breast cancer. Additionally, pesticide exposure also leads to higher disease recurrence and chemoresistance as compared to unexposed individuals. (See Daily News here.)
Women with occupational pesticide exposure have elevated rates of breast cancer, according to a study in Immunopharmacology and Immunotoxicology. Based on an analysis of clinicopathological data from 188 affected women, the study authors demonstrate “that occupational exposure to pesticides modifies the clinical presentation of disease in breast cancer patients, depending on their age at disease onset, affecting cytokine production, especially in those exhibiting early age at diagnosis.” (See Daily News here.) A study published in Ecotoxicology and Environmental Safety finds that the commonly used herbicide, atrazine, promotes breast cancer development through suppression of immune cell stimulation and thus function, and upregulation of enzymes mediating tumor development. (See Daily News here.) The endocrine-disrupting potential of pesticides for breast cancer is of serious concern. For example, a study published in Chemosphere adds to the growing body of research demonstrating the endocrine (hormone) disrupting effects that glyphosate has on breast cancer development. Exposure to the herbicide glyphosate and other glyphosate-based herbicides (GBHs) at high concentrations mimics the estrogen-like cellular effects of the powerful naturally occurring estrogen17β-estradiol (E2), altering binding activity to estrogen receptor α (ERα) sites, thus causing fundamental changes in breast cancer cell proliferation (abundance). (See Daily News here.)
Published in Science of The Total Environment in May 2024, researchers conducted a comprehensive literature review of population-based studies that find strong linkages between direct and acute pesticide exposure and elevated risk of breast cancer (BC). Insecticides—specifically malathion, chlorpyrifos, terbufos, chlordane, and dieldrin—are the predominant group of pesticides in the studies reviewed; however, Carolina Panis, PhD, and coauthor Bernardo Lemos, PhD, indicate the need to track the life-long exposure implications for female agricultural workers and pesticide applicators on other widely-used pesticides, including atrazine and glyphosate. “Ten of the eleven selected studies reported at least one significant association between some aspect of pesticide exposure and BC risk,” the researchers report in summarizing their results. (See Daily News here.)
Call to Action
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Beyond Pesticides engages with communities and local governments across the nation through the Parks for a Sustainable Future Program to transition public parks and playing fields to organic land management. You can become a Parks Advocate today and bring about the organic transition to your community!
To review additional research on the relationship between pesticides and public health, please visit the Pesticide-Induced Diseases Database, including the section on breast cancer.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Cancer Causes & Control
