Kenneth Bodner

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.

We thank Villeneuve and Steenland for their comments (1) on our study (2) that examined the mortality experience of workers exposed to 2,3,7,8-tetrachlrodibenzo-p-dixoin. Villeneuve and Steenland raise 3 concerns about the completeness of our study analyses, including evaluating latency, examining alternative models of exposure response, and providing more information on the distribution of exposure estimates. As most journal papers, our paper did not present all the analyses done. We are pleased to provide comments and details on additional analyses that we feel address these concerns.