Melanoma, a cancer most often associated with sun exposure and individual risk factors, appears to follow the contours of Pennsylvania’s agricultural landscape, according to a new analysis that highlights striking regional differences in incidence. Adults living in counties with more cultivated land and heavier herbicide use had significantly higher melanoma rates, even after researchers accounted for ultraviolet radiation and social vulnerability.

The study, published in November 2025 in JCO Clinical Cancer Informatics, identified a 15-county cluster in South Central Pennsylvania where melanoma incidence among adults ages 50 years and older was 57% higher than in the rest of the state. Counties with larger shares of cultivated acreage and herbicide-treated land consistently showed higher rates, suggesting that agricultural practices may contribute to geographic disparities in melanoma risk.

Melanoma incidence in the United States has tripled since the mid-1970s. Although advances in treatment have improved survival, the disease is still expected to claim thousands of lives this year. Ultraviolet radiation is the leading environmental risk factor, but studies of outdoor workers, including those in agriculture, have produced mixed results. That inconsistency has fueled interest in whether farming-related exposures, such as pesticides, may play a role alongside sun exposure.

To examine that question at the population level, a team of researchers at Penn State College of Medicine conducted an ecologic analysis using county-level data from across Pennsylvania. The team analyzed invasive melanoma incidence from 2017 through 2021 among adults 50 years and older and paired those data with measures of agricultural land use, pesticide application, ambient ultraviolet radiation and socioeconomic vulnerability.

Using geospatial clustering techniques, the researchers identified a statistically significant melanoma hot spot spanning 15 counties in South Central Pennsylvania. Eight of those counties are designated as metropolitan, challenging the assumption that agriculture-related cancer risks are confined to rural areas. Compared with counties outside the cluster, those within it had nearly three times more cultivated land and more than double the proportion of herbicide-treated acreage.

In statistical models adjusted for ultraviolet radiation and social vulnerability, each 10% increase in cultivated land corresponded to a 14% increase in melanoma incidence. A roughly 9% increase in herbicide-treated acreage was associated with a similar 14% rise. Herbicides showed the strongest and most consistent association, while smaller positive associations were also observed for insecticide-, fungicide- and manure-treated land.

The authors noted that the entire high-incidence cluster falls within the 28-county catchment area of the Penn State Cancer Institute. That alignment, they wrote, creates an opportunity to integrate research, outreach and prevention efforts in a region with elevated melanoma burden.

Because the study used an ecologic design, it cannot establish cause and effect or assess individual-level exposures, the authors cautioned. The analysis also could not account for personal behaviors, genetic risk or direct measures of pesticide exposure. Still, the findings add to a growing body of literature linking agricultural practices, particularly pesticide use, with melanoma risk in farming regions.

Taken together, the results support a broader One Health approach to cancer control, one that considers how environmental, occupational and behavioral factors intersect. For agricultural regions such as South Central Pennsylvania, the authors suggest melanoma prevention strategies may need to extend beyond sun protection alone to include safer pesticide practices, environmental monitoring and community-based education tailored to populations affected by agricultural exposure.