Skin cancer cluster found in 15 Pennsylvania counties with or near farmland

UNIVERSTIY PARK, Pa. — Counties in Pennsylvania that contained or were near cultivated cropland had significantly higher melanoma rates compared to other regions, according to a new study led by scientists at Penn State.

Researchers at Penn State Cancer Institute analyzed five years of cancer registry data, 2017 through 2021, and found that adults over the age of 50 living in a 15-county stretch of South Central Pennsylvania were 57% more likely to develop melanoma, the deadliest form of skin cancer, than residents elsewhere in the state. They published their findings today (Nov. 14) in the journal JCO Clinical Cancer Informatics.

The cancer cluster includes both rural and metropolitan counties, meaning risks are not confined to remote areas or reserved for those most exposed to the outdoors, explained Charlene Lam, associate professor of dermatology at Penn State Health and co-author on the paper. The researchers stressed the importance of conducting their work through the "One Health" lens. This framework connects human health to the environment and agricultural systems and recognizes many stakeholders must be involved in finding problems and their solutions. 

“Melanoma is often associated with beaches and sunbathing, but our findings suggest that agricultural environments may also play a role,” she said. “And this isn’t just about farmers. Entire communities living near agriculture, people who never set foot in a field, may still be at risk.”

The usual suspect — sunlight — was considered as a part of the study. But even after adjusting for ultraviolet radiation in Pennsylvania and socioeconomic factors, two patterns stood out: Counties with more cultivated cropland and those with higher herbicide use had significantly higher melanoma rates.

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

The researchers found that for every 10% increase in the amount of cultivated land, melanoma incidence rose by 14% throughout that region. A similar trend appeared with herbicide-treated acreage: a 9% increase corresponded to a 13% jump in melanoma cases.

Lam stressed that exposure isn’t limited to the agricultural workers applying the chemicals, as the materials can drift through the air, settle in household dust and seep into water supplies.

“Our findings suggest that melanoma risk could extend beyond occupational settings to entire communities,” she said. “This is relevant for people living near farmland. You don’t have to be a farmer to face environmental exposure.”

In the paper, the researchers cited other studies that previously linked pesticide and herbicide use with melanoma risk due to the fact that the chemicals have been found to heighten sensitivity to sunlight, disrupt immune function and damage DNA in non-human animals and plants.

Benjamin Marks, first author on the paper who is pursuing a medical degree and a master of public health degree at the Penn State College of Medicine, pointed out that while cropland and increased herbicide use seem to go hand in hand with higher melanoma rates, that doesn’t prove that chemicals commonly used on crops like corn, soybeans and grains cause cancer, but rather the numbers show a link worth investigating.

He explained that studies like this are valuable for identifying patterns, but can’t necessarily pinpoint individual risk.

"Think of this as a signal, not a verdict,” Marks said. “The data suggest that areas with more cultivated land and herbicide use tend to have higher melanoma rates, but many other factors could be at play like genetics, behavior or access to health care. Understanding these patterns helps us protect not just farmers, but entire communities living near farmland.”

Lam said her hope is to better understand the relationship between agricultural practices and public health, as the study’s implications extend beyond Pennsylvania. Similar patterns have been reported in agricultural regions of Utah, Poland and Italy, the researchers noted in the paper.

She encouraged those concerned about their risk to perform regular skin checks, wear sun-protective clothing and sunscreen outdoors. As a next step, Lam is leading follow-up research in the rural communities within the study area to learn more about practices adopted by farmers and understand where exposure risks could be coming from.

"Cancer prevention can’t happen in isolation," Lengerich said. "This study demonstrates the importance of a ‘One Health’ approach, an understanding that human health is deeply connected to our environment and agricultural systems. If herbicides and farming practices are contributing to melanoma risk, then solutions must involve not just doctors, but farmers, environmental scientists, policymakers and communities working together."

Other co-authors include Jiangang Liao, professor of public health sciences at Penn State College of Medicine; and Camille Moeckel, fourth-year medical student and research associate at Penn State College of Medicine.

The research was supported by the MPH Capstone Program and the Medical Student Research Project at the Penn State College of Medicine, as well as the University’s Algin B. Garrett Professorship.