Abstract
Despite showing no evidence of carcinogenicity in laboratory animals, the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been associated with non-Hodgkin lymphoma (NHL) in some human epidemiology studies, albeit inconsistently. We matched an existing cohort of 2,4-D manufacturing employees with cancer registries in three US states resulting in 244 cancers compared to 276 expected cases. The Standardized Incidence Ratio (SIR) for the 14 NHL cases was 1.36 (95% Confidence Interval (CI) 0.74–2.29). Risk estimates were higher in the upper cumulative exposure and duration subgroups, yet not statistically significant. There were no clear patterns of NHL risk with period of hire and histology subtypes. Statistically significant results were observed for prostate cancer (SIR = 0.74, 95% CI 0.57–0.94), and “other respiratory” cancers (SIR = 3.79, 95% CI 1.22–8.84; 4 of 5 cases were mesotheliomas). Overall, we observed fewer cancer cases than expected, and a non statistically significant increase in the number of NHL cases.
Highlights
The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is not genotoxic and has shown no evidence of carcinogenicity in laboratory animals [1,2,3,4,5]
The carcinogenicity of 2,4-D in humans has been actively debated since an early case-control report of non-Hodgkin lymphoma (NHL) and herbicide use by farmers [6]
To maintain privacy of the cancer cases, all analyses were conducted by the Michigan Department of Community Health (MDCH) and no identifiable case data were released to the company investigators
Summary
The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is not genotoxic and has shown no evidence of carcinogenicity in laboratory animals [1,2,3,4,5]. The carcinogenicity of 2,4-D in humans has been actively debated since an early case-control report of non-Hodgkin lymphoma (NHL) and herbicide use by farmers [6]. The carcinogenicity of 2,4-D continues to be examined in epidemiology studies. Cancer mortality rates of The Dow Chemical Company 2,4-D workers in Midland, Michigan have been examined previously [8,9,10]. The purpose of this study was to evaluate the cancer incidence rate in these 2,4-D workers since the last evaluation. The use of incidence data may afford greater statistical power than mortality because of the additional surviving cases, while at the same time avoiding some potential disease misclassification and treatment biases sometimes seen in mortality studies [11]
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