Colorectal cancer is no longer a condition that primarily affects older adults. It is now the leading cause of cancer-related deaths among people under 50, and the numbers have been climbing steadily. Globally, early-onset colorectal cancer has increased at a rate of 1.4% annually, and roughly 1 in 5 diagnoses now occur in people under 55. Researchers have been working to understand why, and a recent study published in Nature Medicine has added a significant and unexpected piece to that puzzle.
The findings point toward environmental exposure, specifically a widely used agricultural herbicide, as a potential contributor to the trend. The association had not been identified before, and it is already reshaping how some researchers think about cancer risk in younger populations.
The exposome gave researchers a new way to look at risk
To understand how the study approached the problem, it helps to know what the exposome is. The term refers to the full range of environmental exposures a person accumulates over a lifetime, everything from what they eat and breathe to what chemicals they come into contact with through their food, water, or surroundings.
The research team analyzed epigenetic changes, specifically patterns of DNA methylation, in people diagnosed with colorectal cancer before and after age 50. Epigenetic changes are chemical modifications that affect how genes are expressed without altering the underlying DNA sequence. They function like annotations layered on top of a text, changing how information is read without changing the words themselves.
By mapping those annotations against known lifestyle and environmental factors, the researchers were able to build epigenetic risk scores tied to specific exposures.
Picloram emerged as a finding no one anticipated
The study confirmed several risk factors that researchers expected to find, including tobacco use and certain dietary patterns. What it also found was an association that nobody had predicted. The herbicide picloram, used widely in agriculture, showed a correlation with early-onset colorectal cancer rates that held up even after the researchers accounted for socioeconomic variables.
Counties with higher rates of picloram use also had elevated rates of early-onset colorectal cancer. That geographic overlap, combined with the epigenetic signatures the study identified, made the finding difficult to dismiss as coincidental.
Dr. José Seoane, lead author and researcher at the Vall d’Hebron Institute of Oncology, described the picloram finding as genuinely surprising. Smoking and diet were anticipated. A specific herbicide showing up in the data with this kind of geographic and biological correlation was not.
Correlation is not causation but the signal is strong enough to matter
The study does not establish that picloram causes colorectal cancer. What it establishes is a correlation, one that is specific enough and consistent enough to warrant serious follow-up research. That distinction matters scientifically, but it does not make the finding less significant from a public health perspective.
What the research does clarify is that the drivers of early-onset colorectal cancer are likely environmental in ways that go beyond the usual conversation about diet and exercise. Pesticide exposure is not typically part of how average adults think about their cancer risk, and this study suggests it probably should be.
Dr. Seoane also noted that the modifiable risk factors identified in the study, diet and tobacco use chief among them, represent real opportunities for prevention that do not require waiting for further research. Those levers exist now and the evidence for acting on them is already strong.
What this means for how cancer prevention is approached
The broader implication of the research is methodological as much as it is clinical. Using epigenetic signatures to connect real-world environmental exposures to cancer risk opens a framework that could be applied to other conditions and other chemicals. The exposome concept has been discussed in research circles for years, but studies that operationalize it with this level of specificity are still relatively rare.
The authors called for stronger public health policies targeting environmental exposures and for better prevention strategies built around this kind of data. For a cancer that is becoming more common in younger adults at a rate that has no clear single explanation, that kind of systemic approach may be the most productive path forward.
Colorectal cancer screening in the United States currently recommends that average-risk adults begin at age 45. The trends this study is responding to suggest that the conversation about who is at risk and why needs to expand well beyond age-based guidelines.
