Cancer Cluster Spans 15 PA Counties, New Study Finds

A major skin cancer cluster was found in Pennsylvania counties that were near cultivated farmland, researchers at Penn State University discovered recently, suggesting a connection between cancer and certain agricultural processes.

Rates of melanoma, the deadliest form of skin cancer, were up 57 percent in adults over 50 across a 15-county region. The impacted area covers a large swath of the south-central part of the state.

"Pesticides and herbicides are designed to alter biological systems,” Eugene Lengerich, emeritus professor of public health sciences at Penn State and senior author on the paper, said in a statement. “Some of those same mechanisms, like increasing photosensitivity or causing oxidative stress, could theoretically contribute to melanoma development."

For every 10 percent increase in the amount of cultivated land in a given area, melanoma rates increased by 14 percent, according to the study. And for every 9 percent increase in herbicide usage, melanoma increased by 13 percent.

Researchers said that exposure to these chemicals is not restricted to the actual farm workers handling them, as the materials drift through the air, enter homes, and infect the water supply. Both rural and metropolitan areas were impacted, including several major cities and densely populated suburban areas.

Previous studies have linked herbicides to heightening sensitivity to sunlight and disrupting immune function, scientists said. Similar links to cancer in broad communities near farmland have been found in places as disparate as Utah, Poland, and Italy.

These increases were noted after already considering other risk factors, like exposure to sunlight and socioeconomic status, the study noted.

The "hotspot" counties with the highest rates of skin cancer increases were York, Adams, Franklin, Cumberland, Dauphin, Perry, Mifflin, Juniata, Montour, Northumberland, Union, Synder, Lycoming, Centre, and Columbia.

Authors recommended concerned residents continue taking the steps that are always advised to groups at risk for skin cancer: perform regular skin checks and wear protective clothing outdoors.

Efforts have been underway at the state level for years to ban various herbicides and pesticides. One substance in particular, the toxic weedkiller paraquat, has been banned in 70 countries and has been the focus of environmentalists in Pennsylvania in recent years, according to the Environmental Working Group. However, nothing nearing a ban or tighter restriction has been advanced.

The study, from scientists at the Penn State Cancer Institute, analyzed five years of cancer registry data from 2017 to 2021.

Read the full study in the journal JCO Clinical Cancer Informatics.