Cancer incidence among imazethapyr-exposed pesticide applicators in the agricultural health study cohort

B115

Background:Imazethapyr is a widely used crop herbicide first registered for use in 1989. Although it is extensively used, little is known regarding its cancer risk in humans. Objectives: We evaluated cancer risk from imazethapyr exposure among pesticide applicators enrolled in the Agricultural Health Study (AHS) cohort. Methods: The AHS is a cohort of 57,311 pesticide applicators in North Carolina and Iowa, enrolled from 1993-1997 and followed for cancer through 2004. A comprehensive questionnaire collected information on exposure to imazethapyr and potential confounders. Among the 49,398 licensed pesticide applicators eligible for analysis, 20,646 reported use of imazethapyr. Imazethapyr exposure was classified by intensity-weighted cumulative exposure days (IWED), calculated as [years of use x days per year x intensity level]. Poisson regression analysis was used to calculate rate ratios (RR) and 95% confidence intervals (CI) to evaluate the association of imazethapyr exposure among 2,907 incident cases of cancer. Results: Our results show a small increase in overall cancer risk with increasing imazethapyr use (RR=1.13, 95% CI 0.96, 1.34) when the highest exposed was compared with the nonexposed group. We observed a statistically significant increased risk for bladder cancer (RR=2.37, 95% CI 1.20- 4.68, p for trend 0.01) and colon cancer (RR=1.64, 95% CI 1.00- 2.69, p for trend 0.05) when the highest exposed was compared with the nonexposed group. We did not observe an association among prostate, lung, melanoma, rectal, kidney, oral, pancreas, or lymphohematopoietic cancers. Conclusion: Occupational exposure to imazethapyr, an aromatic amine, was significantly associated with bladder and colon cancer in the AHS cohort. Replication of these results, however, and continued follow-up of this cohort is needed to confirm these findings.