08
Jul
More Studies Link Breast Cancer to Pesticide Exposure, Rates High as Supreme Court Professes Public Protected
(Beyond Pesticides, July 8, 2026) This piece reports on yet additional new studies linking pesticides to breast cancer. A number of recent reviews make it clear that pesticide exposure per se raises the risk of breast cancer, across a wide swath of pesticide types. One would think that with the body of science linking breast cancer with pesticide exposure, covered extensively by Daily News and the Pesticide-Induced Diseases Database, a scientific-based regulatory system would respond with a sense of urgency. And yet, that is not the case, as the U.S. Environmental Protection Agency (EPA) establishes acceptable rates of disease for individual chemicals or chemical families, but does not evaluate patterns of disease linked to multiple chemical exposure. And so, breast cancer is the most common cancer diagnosed in U.S. women, and women turn to medical intervention with drugs, early surgical intervention, and targeted radiation. Yet, the disease, principally associated with environmental rather than hereditary factors, and treatment cause severe disruption to the lives of women and their loved ones, is devastating to quality of life, while clinical responses can have adverse side effects.
Many different pesticides affect cellular processes and structures, including alteration of genetic material, endocrine disruption, cell apoptosis, cell signaling disruption and oxidative stress. Breast tissue is perhaps one of the most sensitive of all organs to the insults of pesticide exposure, in part because it accumulates lipophilic chemicals. Nearly 400,000 women will be diagnosed with it this year, and more than 40,000 will die. In the U.S. and globally, 80% of women have no specific risk factors beyond sex and age; family history accounts for only a small percentage of cases. While mortality has been dropping in high-income countries, incidence in the U.S between 2010 and 2019 increased at 0.5% per year.
The world recently read a U.S. Supreme Court ruling in Monsanto v. Durnell (June 25, 2026) that exclaimed, “[B]efore registering a pesticide, EPA must evaluate a pesticide and its proposed label—and must determine that the proposed label incudes all warnings necessary and adequate to protect human health and the environment. . .” Continuing, the Court majority professes, “. . .EPA critically evaluates the pesticide’s label to ensure that the label contains all warnings necessary to protect human health.” And, it does this without requiring a warning about the potential risk of breast cancer, or other types of cancer and chronic effects. Some have characterized the Court’s ruling as spinning a narrative, including former EPA officials, who submitted to the Court an amicus brief.
While the pesticide connection to breast cancer is broad, recent studies have linked the disease to exposure to the insecticide chlorpyrifos, a chemical widely used in agricultural food production, including soybeans, fruit and nut trees, broccoli, cauliflower, and other row crops, as well as for public health mosquito control and on golf courses. A study reported at a scientific meeting by a group of Indian researchers examined breast cancer tissues for pesticide residues, finding 49 distinct organophosphate residues in both tumor tissue and surrounding adipose tissue. Organophosphates (OP), long considered primarily neurotoxicants, have also been associated with cancer. While chlorpyrifos is the most prominent example, due to its enormous global use, the class also includes acephate, diazinon, dimethoate, and others. A study of more than 30,000 spouses of pesticide applicators analyzed in a report by Pamela Ferdinand of U.S. Right to Know found that “Any OP use was associated with an elevated risk of breast cancer” (emphasis added).
Organophosphates may also contribute to breast cancer induction indirectly through gut microbiota. Scientists at two Chinese institutions found that, in mice, chlorpyrifos exposure at environmentally relevant levels elevated certain gut microbes’ metabolites, and these promoted breast tumor growth. While mammals can detoxify organophosphate compounds to some degree, gut microbes are far more vulnerable. “The alterations in gut microbe-derived metabolites resulting from chlorpyrifos exposure may significantly contribute to the promotion of breast tumor growth, even at environmental doses,” the authors write. Other studies have shown that chronic low-dose exposure shortens tumor latency and contributes to the proliferation of estrogen-dependent breast cancer cells.
Clearly, all women are at considerable risk of contracting some form of breast cancer, and there are some subgroups at even higher risk. For African-American and Hispanic women, breast cancer is the leading cause of cancer deaths. Studies of occupational exposures, especially in agriculture, show that women working in and living near agricultural operations have a significantly greater risk of contracting breast cancer than those in other developed environments. Women in agricultural areas are often diagnosed with more aggressive forms of breast cancer, according to a study led by Carolina Panis, PhD, of women in the Parana region of Brazil analyzed in the February 26 Daily News Blog. A 2024 Brazilian study found that among women with early-onset breast cancer (under 50 years old at diagnosis), exposure to pesticides led to more severe disease and raised the risk of recurrence and death.
A study by Dr. Panis and colleagues in Brazil and the University of Arizona found that glyphosate and atrazine in drinking water at levels below or within maximum residue levels in the U.S and Brazil altered breast cancer cells’ RNA expression, DNA repair and cell metabolism. Gene expression was different between lower and higher doses. “Our findings indicate that low-level glyphosate and atrazine exposures induce subtle structural and transcriptomic changes without overt cytotoxicity,” the authors write. These changes may affect breast cancer induction and progression.
Similarly, a Chilean in vitro study exposed estrogen receptor sensitive and triple-negative breast cancer cells to low-dose glyphosate for eight weeks. The cells tended to lose their anchorage, migrate, and exhibit enhanced resistance to doxorubicin, a chemotherapeutic agent. “These findings indicate that sustained exposure to glyphosate, at a concentration within the reported human exposure range, is associated with features consistent with a cancer stem [cell]-like and adaptive phenotype in breast cancer cells,” the authors write.
Pyrethrins, touted as “safe” insecticides because of their low acute toxicity in mammals, are used against numerous household and garden pests. An innovative Chinese study used machine learning to analyze chemical data on the relationships between cellular compounds and various pyrethrin compounds. The researchers found numerous proteins and enzymes “capable of influencing multiple carcinogenic pathways,” [with] “broad toxicological significance and highlighting the need for further risk assessment in environmental and pharmaceutical contexts,” including “oncogenic potential toward breast cancer-related proteins.”
One of the ironies of the pesticide problem is that consumption of fruits and vegetables in general is an excellent way to lower cancer risk, but fruits and vegetables are the principal way people are exposed non-occupationally to pesticides. With respect to breast cancer in particular, a striking study by researchers from the Sorbonne and Aix Marseille University in France found a direct link between organic fruit and vegetable consumption and reduction of postmenopausal breast cancer. The researchers followed more than 31,000 people, 75% of them female, for an average of 7.3 years. They note that occupational associations between pesticides and cancer are well established, but dietary exposure data are much murkier. They state that only three studies directly investigated consumption of organic foods and cancer risk, and the results were conflicting. The British Million Women Study found a slightly raised risk of breast cancer among consumers of organic food, while a Danish study found lower risk of stomach cancer and slightly higher risk of non-Hodgkin lymphoma. All the cited studies used “relatively rudimentary questions about the frequence of organic consumption.”
To refine the questionnaire method and clarify the issue, the French researchers derived their data from the Nutri-Net-Santé cohort of French residents, a web-based questionnaire program begun in 2009. The study collects detailed demographic information along with “a self-administered semiquantitative food frequency questionnaire…aiming to assess organic (i.e., complying with official European Union standards and carrying the European label) and conventional food consumption.” To assess the consistency of self-reported estimates, they compared this information to data from previous research that included urinary biomarkers of pesticide exposure, which would indicate the relative consumption of organic versus non-organic fruits and vegetables.
The researchers found a robust relationship between organic fruit and vegetable consumption and reduced risk of postmenopausal breast cancer. For each 100 grams per day of organic foods substituted for non-organic, there was a 10% reduction of risk.
There are many issues with determining the clarity of such studies, as the authors note. People who eat mostly organic may have other habits healthier than the general population, and tend toward higher consumption of fruits and vegetables overall. The authors cite a large U.S. study finding no association between highly contaminated fruits and vegetables and overall cancer risk except glioma, but importantly, that study also found a “marked reduction in the risk of death with elevated consumption of low-contaminated fruits and vegetables,” along with a 36% reduction in the risk of all-cause mortality among high consumers of uncontaminated produce.
It is clear that eating organic food is the most direct way to reduce the numerous risks associated with pesticides, despite the murky results of some studies. One in eight women will be diagnosed with breast cancer in her lifetime; the disease comprises a third of all cancer diagnoses in women annually. For women, exposure to toxic chemicals creates not only physical distress and financial burdens, but also enormous anxiety, particularly about breast cancer, for which the purveyors of such chemicals bear heavy responsibility.
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.
Sources:
Consumption of organic compared with conventional fruits and vegetables in relation to cancer risk: findings from the NutriNet-Santé cohort study
Berlivet et al.
The American Journal of Clinical Nutrition 2026
https://www.sciencedirect.com/science/article/pii/S0002916526000936?via%3Dihub=
Nearly 300 studies link the common pesticide chlorpyrifos to multi-organ damage, DNA disruption, and chronic disease
Pamela Ferdinand
U.S. Right to Know 2026
https://usrtk.org/healthwire/chlorpyrifos-multi-organ-damage-dna-disruption-and-chronic-disease/
Beyond Pesticides
Breast Cancer Archive
https://www.beyondpesticides.org/resources/pesticide-induced-diseases-database/search-the-database?cat45=45&catcount=1&searchlogic=OR&searchbutton=SEARCH
An integrated environmental toxicity risk assessment framework combining deep learning and molecular simulation: A case study on pyrethrins and breast cancer
Sung et al.
Biochemistry and Biophysics Reports 2025
https://www.sciencedirect.com/science/article/pii/S2405580825002286?via%3Dihub
Environmental-dose chlorpyrifos disrupts gut microbiota and microbial metabolite profiles: An indirect mechanism promoting breast tumor growth
Yuan et al.
Journal of Environmental Sciences 2026
https://www.sciencedirect.com/science/article/abs/pii/S1001074225007090
Genome-wide gene expression changes in breast cancer cells following very low-dose exposure to pesticides (glyphosate and atrazine) at drinking water levels
Panis et al.
Environmental Toxicology and Pharmacology 2025
https://www.sciencedirect.com/science/article/abs/pii/S1382668925001772?via%3Dihub
Effect of pesticides on breast cancer tumor
Marcoccia et al.
BMC Biology Direct 2026
https://link.springer.com/article/10.1186/s13062-025-00709-9
Detection of organophosphorus pesticide residues in breast cancer tissue: A translational integrated environmental exposure study.
Sekar et al.
Journal of Clinical Oncology 2026
https://ascopubs.org/doi/pdf/10.1200/JCO.2026.44.16_suppl.e12580
Chlorpyrifos and Chlorpyrifos-Oxon: A Widening Spectrum of Toxicity
Kalenik et al.
International Journal of Molecular Science 2026
https://pmc.ncbi.nlm.nih.gov/articles/PMC13164365/
