Occupational exposure to terbufos and the incidence of cancer in the agricultural health study

Objective Terbufos is the fourth most commonly used organophosphate insecticide (OP) in the United States. Terbufos has not been demonstrated to be carcinogenic in rodents, although non-arsenical insecticides, including OPs, have been associated with excess cancer in epidemiologic studies. We investigated associations between use of terbufos and the incidence of cancer. Methods The Agricultural Health Study is a prospective cohort study of 57,310 licensed pesticide applicators from Iowa and North Carolina. Detailed information about 50 pesticides, including terbufos, and potential confounders was obtained from self-administered questionnaires. Terbufos intensity-weighted lifetime exposure-days were defined as (lifetime exposure-days) × (exposure intensity score). Cases include all first primary cancers diagnosed between enrollment and December 31, 2005. Hazard ratios (HR) and 95% CI were calculated with Cox proportional hazards models, adjusting for potential confounders. Results Overall cancer risk was slightly increased among terbufos users [HR 1.21 (1.06-1.37)]. Suggestive associations were observed between terbufos use and cancers of the prostate (HR_{highest tertile} = 1.21; 95% CI = 0.99-1.47) and lung (HR_{middle tertile} = 1.45; 95% CI = 0.95-2.22) and leukemia (HR_{middle tertile} = 2.38; 95% CI = 1.35-4.21) and non-Hodgkin's lymphoma (HR_{middle tertile} = 1.94; 95% CI = 1.16-3.22), although the exposure-response gradients were non-monotonic and p for trends were not significant. Conclusion We found suggestive associations between occupational terbufos use and several cancer sites. However, cautious interpretation of these results is warranted by the lack of existing experimental and epidemiologic evidence to support carcinogenic effects of terbufos.