Pesticide exposure and cancer

Pesticide exposure is an area of ongoing research in cancer epidemiology, with associations proposed for non-Hodgkin lymphoma, leukaemia, breast cancer, prostate cancer, kidney cancer, and pancreatic cancer. The evidence is strongest for occupational exposure in agricultural workers, where cumulative exposures can be substantially higher than in the general population through residential proximity or dietary residues. The cancer types most implicated vary by pesticide class and exposure type.

Pesticides represent a heterogeneous group of chemical compounds including organophosphates, organochlorines, carbamates, pyrethroids, and triazines. Organochlorine pesticides, including DDT and lindane, are persistent organic pollutants that bioaccumulate in fatty tissue and act as endocrine disruptors by mimicking or modulating oestrogen signalling, potentially promoting hormone-sensitive cancers. Some pesticides cause direct DNA damage and oxidative stress, while others suppress immune function or promote chronic inflammation. Organophosphate flame retardants and insecticides have been shown to alter gene expression and signalling pathways relevant to carcinogenesis: one study found that 2-ethylhexyl diphenyl phosphate (EHDPP), an organophosphate ester, stabilised epidermal growth factor receptor (EGFR) expression in lung cells through network toxicology analysis, potentially accelerating lung cancer progression. Plasma organophosphate ester levels in healthy adults were associated with altered microRNA (miRNA) expression profiles, suggesting early molecular perturbation from environmental exposure levels below those causing overt toxicity.

A scoping review of breast cancer and environmental pollutants found associations with several industrial chemicals and agricultural pesticides, though most evidence came from retrospective study designs with variable quality, limiting causal inference. An analysis of the French AGRICAN (AGRIculture and CANcer) cohort of approximately 180,000 agricultural participants found that certain agricultural activities and specific occupational exposures were associated with kidney cancer risk, with 654 incident kidney cancer cases identified over the follow-up period. A Brazilian study found that women with occupational or household pesticide exposure had a higher frequency of the more aggressive Luminal B breast cancer subtype and poorer prognostic features at diagnosis compared to unexposed women, suggesting that pesticide exposure may not merely increase cancer incidence but may also influence tumour biology. A systematic review of occupational cancers in the Indian subcontinent identified pesticide exposure as a significant concern for agricultural workers, with associations reported for multiple cancer types.

Agricultural workers with direct pesticide application duties face the highest occupational exposures, often cumulated over decades without adequate protective equipment in some regions. Women working in conventional agriculture may face elevated breast cancer risk, and prenatal or early childhood exposures may carry particular vulnerability given developmental sensitivity of the endocrine and immune systems. Rural populations in countries where older, more toxic pesticide formulations remain in legal use face greater risk than urban populations or those in countries with strong regulatory frameworks eliminating the most hazardous compounds.

The evidence linking pesticide exposure to cancer is mixed and complicated by substantial methodological challenges including difficulty measuring precise cumulative exposures, long latency periods between exposure and cancer diagnosis, and wide variation in the types and formulations of pesticides in use across settings and time periods. IARC has classified specific pesticides including lindane (Group 1) and glyphosate (Group 2A) as human carcinogens or probable carcinogens, but general pesticide exposure cannot be assigned a single risk classification because the category is too heterogeneous. The strongest evidence is for occupational exposure and non-Hodgkin lymphoma, and for certain organochlorine compounds and breast cancer risk in agricultural settings.

Evidence indicates that occupational pesticide exposure, particularly chronic agricultural exposure to certain organochlorine and organophosphate compounds, is associated with increased cancer risk for some cancer types. For the general population, exposures through food residues are substantially lower than occupational levels, and the associated cancer risk remains uncertain. Risk likely depends heavily on the specific compounds involved, the duration and intensity of exposure, and individual genetic susceptibility in carcinogen metabolism.