Abstract 837: Carbaryl use and cancer incidence in the agricultural health study - An updated analysis
Authors: Erickson Patricia A. , Andreotti Gabriella , Remigio Richard , Parks Christine G. , Sandler Dale P. , Albert Paul S. , Barry Kathryn H. , Hofmann Jonathan N. , Beane Freeman Laura E. 
Published: March 2024

Background: Carbaryl is a carbamate insecticide with widespread residential and agricultural uses. Previous epidemiologic investigations, including in the Agricultural Health Study (AHS), have suggested potential associations between carbaryl use and cancer risk. In this analysis, we updated a previous AHS evaluation of carbaryl and cancer risk by incorporating additional exposure information and follow-up time.

Methods: The AHS is a prospective cohort study of licensed pesticide applicators in North Carolina (NC) and Iowa (IA). Information on lifetime pesticide use, including carbaryl, was reported on questionnaires at enrollment (1993-1997) and follow-up (1999-2005). We evaluated cancer risks associated with ever-use and intensity-weighted lifetime days (IWLD) of carbaryl use, comparing those who reported use to those who did not. For IWLD, carbaryl exposure was categorized (quartiles, tertiles, or the median) among users, depending on the number of cases. Among 52,625 applicators, 8,713 incident cancers were identified from linkages with state cancer registries through 2014 (NC) or 2017 (IA). We used Poisson regression to estimate risk ratios (RR) and 95% confidence intervals (CI), controlling for confounders, and evaluated lagged exposures.

Results: Approximately 50% of applicators reported use of carbaryl. Among cancer cases, 53% reported carbaryl use. Increasing IWLD of carbaryl use was associated with stomach cancer (RRT3=2.15, 95% CI: 1.11-4.15, p-trend=0.02), which persisted across lags up to 15 years. Carbaryl users in the highest quartile of IWLD had an increased risk of leukemia (RRQ4=2.12, 95% CI: 1.05-4.29, p-trend=0.08); this risk remained elevated, though attenuated, when exposure was lagged by 5-years (RRQ4=1.86, 95% CI: 0.91-3.81, p-trend=0.14). Ever-use of carbaryl was also suggestively associated with both esophageal (RR=1.45, 95% CI: 0.98-2.14) and tongue (RR=1.87, 95% CI: 0.93-3.74) cancers.

Conclusion: This study provides novel evidence of associations between carbaryl use, leukemia, and stomach cancer, as well as suggestive evidence of elevated risks of esophageal and tongue cancers. With more than 7,000 added cancer cases and up to 14 additional years of follow-up time as compared to a previous analysis in the AHS, we were able evaluate cancer sites not previously examined, making this the largest prospective study of carbaryl and cancer risk to date. Our findings highlight the need for additional studies of this widely used insecticide.

Citation Format: Patricia A. Erickson, Gabriella Andreotti, Richard Remigio, Christine G. Parks, Dale P. Sandler, Paul S. Albert, Kathryn H. Barry, Jonathan N. Hofmann, Laura E. Beane Freeman. Carbaryl use and cancer incidence in the agricultural health study - An updated analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 837.