22 pesticides show link to prostate cancer

Nearly two dozen pesticides are linked to an increased risk of prostate cancer in the United States, researchers report Nov. 4 in cancer. Four of them, the study finds, are also linked to prostate cancer deaths.

The findings cannot say for sure that these pesticides caused prostate cancer, says John Leppert, a urologist at Stanford University School of Medicine. It is not known whether the men who were diagnosed with prostate cancer in Leppert’s data were exposed to pesticides.

“This study is really the best one to find potential pesticides that might be linked to prostate cancer,” says Leppert, “so we can narrow down the list of things to study further.”

Despite being the second most common cancer in the United States, some prostate cancer risk factors remain elusive (SN: 16/10/19). “Your risk of developing prostate cancer or other cancers varies in the United States depending on where you live, and we don’t yet have good explanations for this geographic variation,” says Leppert.

Some pesticides are thought to increase the risk of prostate cancer, but previous studies have been inconclusive: they have focused on small geographic areas or only a few pesticides. So Leppert and colleagues looked at data on prostate cancer incidence and use of nearly 300 pesticides in more than 3,100 US counties.

Counties with a higher use of 22 specific pesticides, after adjusting for characteristics such as age distribution, were more likely to have more cases of prostate cancer or death several years after pesticide use.

The team analyzed pesticide use and cancer outcomes over 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 examined pesticide use from 2002 to 2006 and cancer incidence from 2016 to 2020.

The long delay between pesticide use and cancer detection exists because prostate cancer takes time to progress, Leppert says. The 22 pesticides showed associations with prostate cancer incidence in both time periods. This included pesticides known as 2,4-D, a herbicide often used to treat weeds.

“As a clinician, I hope that as we understand it [environmental exposures] better, then we can be better doctors for our patients,” says Leppert. “Hopefully, our understanding of a patient’s environment will help us catch prostate cancer early and, if necessary, treat it better.”