Researchers have found that nearly two dozen pesticides are associated with an increased risk of prostate cancer in the United States, four of them also being tied to prostate cancer deaths.
Among them is the toxic 2,4-D, a water-soluble herbicide that controls broadleaf weeds and germinating grasses in crops like barley, maize, potatoes and wheat, and which is frequently used in South Africa, despite calls for its prohibition.
Although their findings “can’t say for certain that these pesticides caused prostate cancer”, said John Leppert, a urologist at Stanford University School of Medicine, and it’s unknown whether those diagnosed with prostate cancer in the data were exposed to the pesticides, “this study is really best at finding the potential pesticides that may be linked with prostate cancer so we could narrow the list of things needing to be further studied.”
Despite being the second most common cancer in the US, some risk factors of prostate cancer remain elusive.
“Your risk of developing prostate cancer or other cancers varies in the US depending on where you live, and we don’t have good explanations for that geographic variation yet,” Leppert added.
A few pesticides are thought to increase prostate cancer risk, but prior studies have been patchy, focusing on small geographic areas or just a few pesticides. So Leppert and colleagues looked at data on prostate cancer incidence and the use of nearly 300 pesticides in more than 3 100 American counties.
Counties with a higher use of 22 particular pesticides, after adjustment for characteristics such as age distribution, were more likely to have more prostate cancer cases or deaths several years after the pesticides were used, according to their findings, published in Cancer.
The team analysed pesticide use and cancer outcomes in two different time periods. The first period focused on pesticide use from 1997 to 2001 and cancer outcomes from 2011 to 2015. The second period looked at pesticide use from 2002 to 2006 and cancer incidence from 2016 to 2020.
The long lag between pesticide use and cancer discovery exists because prostate cancer takes time to progress, Leppert said.
The 22 pesticides showed links to prostate cancer incidence in both time periods. This included commonly known toxic pesticides like 2,4-D, commonly used to treat weeds and which is highly hazardous.
“As a clinician, I hope that as we understand environmental exposures better, then we can be better doctors to our patients,” he said.
“Our understanding of a patient’s environment will, hopefully, help us to catch prostate cancer early and, if needed, to treat it better.”
Study details
Pesticides and prostate cancer incidence and mortality: An environment-wide association study
Simon Soerensen, David Lim, Maria Montez-Rath et al.
Published in Cancer on 4 November 2024
Abstract
Background
Prostate cancer is the most common cancer among men in the United States, yet modifiable risk factors remain elusive. In this study, the authors investigated the potential role of agricultural pesticide exposure in prostate cancer incidence and mortality.
Methods
For this environment-wide association study (EWAS), linear regression was used to analyse county-level associations between the annual use of 295 distinct pesticides (measured in kg per county) and prostate cancer incidence and mortality rates in the contiguous United States. Data were analysed in two cohorts: 1997–2001 pesticide use with 2011–2015 outcomes (discovery) and 2002–2006 use with 2016–2020 outcomes (replication). The reported effect sizes highlight how a 1-standard-deviation increase in log-transformed pesticide use (kg per county) corresponds to changes in incidence. Analyses were adjusted for county-level demographics, agricultural data, and multiple testing.
Results
Twenty-two pesticides showed consistent, direct associations with prostate cancer incidence across both cohorts. Of these, four pesticides were also associated with prostate cancer mortality. In the replication cohort, each 1-standard-deviation increase in log-transformed pesticide use corresponded to incidence increases per 100,000 individuals (trifluralin, 6.56 [95% confidence interval (CI), 5.04–8.07]; cloransulam-methyl, 6.18 [95% CI, 4.06–8.31]; diflufenzopyr, 3.20 [95% CI, 1.09–5.31]; and thiamethoxam, 2.82 [95% CI, 1.14–4.50]). Limitations included ecological study design, potential unmeasured confounding, and lack of individual-level exposure data.
Conclusions
The results of this study suggest a potential link between certain pesticides and increased prostate cancer incidence and mortality. These findings warrant further investigation of these specific pesticides to confirm their role in prostate cancer risk and to develop potential public health interventions.
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