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Insecticide Use and Breast Cancer Risk among Farmers’ Wives in the Agricultural Health Study

Lawrence S. Engel, Emily Werder, Jaya Satagopan, Aaron Blair, Jane A. Hoppin, Stella Koutros, Catherine C. Lerro, Dale P. Sandler, Michael C. Alavanja, and Laura E. Beane Freeman
Environmental Health Perspectives (2017) DOI: https://doi.org/10.1289/EHP1295 PMID: 28934092

Publication

Abstract

BACKGROUND: Some epidemiologic and laboratory studies suggest that insecticides are related to increased breast cancer risk, but the evidence is inconsistent. Women engaged in agricultural work or who reside in agricultural areas may experience appreciable exposures to a wide range of insecticides.

OBJECTIVE: We examined associations between insecticide use and breast cancer incidence among wives of pesticide applicators (farmers) in the prospective Agricultural Health Study.

METHODS: Farmers and their wives provided information on insecticide use, demographics, and reproductive history at enrollment in 1993–1997 and in 5-y follow-up interviews. Cancer incidence was determined via cancer registries. Among 30,594 wives with no history of breast cancer before enrollment, we examined breast cancer risk in relation to the women’s and their husbands’ insecticide use using Cox proportional hazards regression to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS: During an average 14.7-y follow-up, 39% of the women reported ever using insecticides, and 1,081 were diagnosed with breast cancer. Although ever use of insecticides overall was not associated with breast cancer risk, risk was elevated among women who had ever used the organophosphates chlorpyrifos [HR=1.4 (95% CI: 1.0, 2.0)] or terbufos [HR=1.5 (95% CI: 1.0, 2.1)], with nonsignificantly increased risks for coumaphos [HR=1.5 (95% CI: 0.9, 2.5)] and heptachlor [HR=1.5 (95% CI: 0.7, 2.9)]. Risk in relation to the wives’ use was associated primarily with premenopausal breast cancer. We found little evidence of differential risk by tumor estrogen receptor status. Among women who did not apply pesticides, the husband’s use of fonofos was associated with elevated risk, although no exposure–response trend was observed.

CONCLUSION: Use of several organophosphate insecticides was associated with elevated breast cancer risk. However, associations for the women’s and husbands’ use of these insecticides showed limited concordance. Ongoing cohort follow-up may help clarify the relationship, if any, between individual insecticide exposures and breast cancer risk.

Figures

Figure 1. Flow diagram showing an analysis of insecticide use and incident breast cancer in wives.

Flow diagram showing the study population for an analysis of insecticide use and incident breast cancer in wives enrolled in the Agricultural Health Study. Boxes with solid lines represent individuals who remained in the analysis after each step, and boxes with dashed lines represent individuals who were excluded after each step. Cancer and mortality follow-up was via registry linkage.

Tables

Table 1. Selected characteristics at enrollment of farmers’ wives.

Selected characteristics at enrollment (unless otherwise noted) of farmers’ wives in the Agricultural Health Study.

Table 2. Associations between the wives’ ever use of individual insecticides and of breast cancer.

Associations between the wives’ ever use of individual insecticides at enrollment and risk of breast cancer among farmers’ wives in the Agricultural Health Study (n=30,594).

Table 3. Associations between the wives’ use of insecticides and risk of breast cancer.

Associations between the wives’ intensity-weighted days per year of use of individual insecticides at the 5-year follow-up and risk of breast cancer among farmers’ wives in the Agricultural Health Study (n=22,271).

Table 4. Associations between the husbands’ use of insecticides and risk of breast cancer.

Associations between the husbands’ use of individual insecticides and risk of breast cancer among farmers’ wives who never used pesticides in the Agricultural Health Study (n=13,500).

Supplemental Materials

Supplemental Material