Abstract A128: Agricultural pesticide usage and breast cancer incidence: An ecological study across US counties

Purpose: We examined associations between county-level pesticide use and breast cancer incidence rates, overall and by metropolitan status, accounting for potential latency between exposure and diagnosis. This study aims to fill critical gaps in understanding the potential role of environmental pesticide exposure on breast cancer risk in diverse geographic settings. Methods: This ecologic study used publicly available data on county-level agricultural pesticide usage (kg) for 38 pesticides with potential endocrine-disrupting properties relevant in breast cancer etiology. We evaluated overall pesticide usage and categorized pesticides according to their chemical structure into the following classes: carbamates, neonicotinoids, organochlorines, organophosphates, phosphonates, pyrethroids, triazines, and other miscellaneous compounds. The analysis included 2,457 U.S counties with information on both pesticide usage (2001-2015) and age-adjusted breast cancer incidence rates (2016-2020). Counties were classified as rural or urban based on the 2013 Rural-Urban Continuum Codes. Gamma regression models with a log-link function were used to estimate associations between pesticide use (per 500,000 kg) and age-adjusted breast cancer incidence rates, adjusting for county-level covariates (smoking, poverty, unemployment, education, and insurance). Trends in pesticide use over time and by rurality were assessed using ANOVA tests for linear trend. Results: Total pesticide use was significantly higher in rural vs. urban counties (49,067 kg vs. 41,356 kg; p<.05), with some variation by pesticide class. Pesticide use was positively associated with breast cancer incidence (b=0.05 (95% CI, 0.001, 0.10)), particularly in rural (b=0.14 (95% CI, 0.06, 0.21)), but not in urban (b=-0.03 (95% CI, -0.08, 0.03) counties (pint <.001). Triazines were positively associated with overall breast cancer rates (b=0.16 (95% CI, 0.001, 0.32)), with slightly stronger associations in rural counties (b=0.38 (95% CI, 0.13, 0.64)). In rural counties, positive associations were also observed for neonicotinoids (b=12.94 (95% CI, 5.48, 20.44)), organochlorines (b=16.32 (95% CI, 3.47, 29.58)), phosphonates (b=0.20 (95% CI, 0.08, 0.32)), and miscellaneous compounds (b=2.55 (95% CI, 0.44, 4.72)). Carbamates, organochlorines, organophosphates, triazines and other miscellaneous pesticides usage decreased over time (all p0<.001), while use of neonicotinoids, phosphonates, and pyrethroids increased (all p<0.05). Conclusion: Our findings point to a possible association between select pesticide classes and increased breast cancer incidence in rural U.S. counties. These results emphasize the critical need for continued research into the biological mechanisms linking specific pesticide classes to breast cancer incidence in rural regions. Future work should incorporate individual-level exposure data and account for the cumulative and synergistic effects of multiple environmental chemicals. Citation Format: Harish Neelam, Furqan Irfan, Robert Wahl, John Clements, Kelly A. Hirko. Agricultural pesticide usage and breast cancer incidence: An ecological study across US counties [abstract]. In: Proceedings of the 18th AACR Conference on the Science of Cancer Health Disparities; 2025 Sep 18-21; Baltimore, MD. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2025;34(9 Suppl):Abstract nr A128.