We included all pesticides with available data (295 in total), aiming to be as comprehensive as possible. We did have to exclude some pesticides that were not commonly used. Many of these chemicals have not been previously studied for their health effects or carcinogenic potential, and even less so for prostate cancer. Using this approach, we wanted to combat publication bias by reporting all associations (whether significant or not) and comparing the relative strength of associations across each pesticide.
This study's strength lies in its ecological design, which enables the examination of hundreds of unique pesticide exposures and their potential associations with prostate cancer. Additional strengths of the study include the use of strict and robust methods to confirm findings. Specifically, we adjusted for multiple testing to reduce false positives, incorporated machine learning to identify variables to adjust for residual confounding, and validated candidate pesticides in a separate cohort. This allowed us to generate hypotheses about potential pesticide and prostate cancer associations for more targeted studies.
Notably, 22 of the studied pesticides were found to be potentially associated with prostate cancer incidence. Among these, four pesticides were found to be potentially associated with prostate cancer mortality. It was surprising that only one of the four pesticides linked to prostate cancer mortality (trifluralin) is classified by the EPA as a possible human carcinogen. These potential associations merit further investigation to explore potential causality and understand the underlying mechanisms of these associations.
This study is one example of a growing field investigating the “exposome”, which studies the complex interactions between multiple environmental exposures and disease. We see this study as the first step to better understand potential pesticide exposure and prostate cancer relationships and to generate hypotheses for future studies whose results may lead to additional pesticides being recognized as possible carcinogens by the EPA and other organizations.
Written by: Simon John Christoph Sørensen, MD1,2 and John T. Leppert, MD, MS1,3,4
- Department of Urology, Stanford University School of Medicine, Stanford, CA, USA
- Department of Epidemiology and Population Health, Stanford University School of Medicine, Stanford, CA, USA
- Division of Nephrology, Department of Medicine, Stanford University School of Medicine, Stanford, CA, USA
- Division of Urology, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA, USA
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