We finally have at least one answer to what's going on with the colorectal cancer incidence in our generation: a pesticide produced by Dow Chemical in 1964. Listened to this discovery on a podcast earlier today, but the specific Nature publication is here: https://www.nature.com/articles/s41591-026-04342-5.
Primary Finding: Picloram Exposure
The most significant finding was a strong association between EOCRC and exposure to picloram, a systemic herbicide used widely for controlling woody plants and broadleaf weeds since the 1960s (often found in commercial products like Tordon).
Correlation: Patients with early-onset colorectal cancer showed significantly higher methylation signatures associated with picloram compared to older patients.
Consistency: This association remained significant even after adjusting for known risk factors like diet, smoking, and socioeconomic status.
Validation: The findings were replicated across nine independent international cohorts, suggesting the link is not an isolated phenomenon.
Geographic and Historical Evidence
To bolster their molecular findings, the researchers analyzed pesticide use data from 94 United States counties over a 21-year period. They found that counties with the highest historical use of picloram also had the highest incidence rates of early-onset colorectal cancer.
The researchers noted that picloram was first registered for use in 1964. People born after this date (who are now in the age range for EOCRC) would have been the first generation exposed to the chemical from early childhood, which may explain why the signature is prevalent in younger patients but less so in those born before its widespread adoption.
Conclusion and Caveats
The study concludes that environmental chemicals, specifically certain herbicides, may be a primary driver of the shifting demographics of cancer. However, the authors emphasize:
Association vs. Causation: The study identifies a strong correlation but does not definitively prove that picloram causes cancer.
Need for Further Research: The researchers call for longitudinal studies and experimental models to determine the exact biological mechanism by which picloram might trigger oncogenic changes in the colon and rectum.
This research represents a significant shift in the study of EOCRC, moving focus away from purely "lifestyle" factors (like diet and sedentary behavior) toward long-term environmental pollutants.