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- Why are young people getting colon cancer? A common weed killer may be linked, scientists say (businessinsider.com)
A recent study published in Nature Medicine points to a possible connection between a widely used herbicide and the growing incidence of colorectal cancer in younger adults under 50-a trend that has puzzled researchers worldwide.
The herbicide in question, picloram, is commonly applied to eliminate woody plants and shrubs while leaving grass unharmed. The study suggests that exposure to picloram may be linked to the rising cases of colon and rectal cancers among younger populations, whereas no significant association was found in colorectal cancer cases among those over 70.
Led by computational biologist Jose Seoane of the Vall d’Hebron Institute of Oncology in Barcelona, the research team analyzed DNA methylation patterns-chemical markers that influence gene activity-in tumor samples. These patterns can act as “fingerprints,” reflecting environmental exposures over a person’s lifetime.
Seoane’s team identified DNA methylation signatures tied to several known risk factors, including smoking, unhealthy diets lacking in Mediterranean staples like fresh vegetables and nuts, obesity, and lower educational attainment. Notably, they also found a signature linked to picloram exposure. Initially skeptical, the researchers conducted further analyses and found no alternative explanations for this association.
Expanding their investigation, the team examined data from seven U.S. states, comparing county-level pesticide usage with rates of young-onset colorectal cancer. Picloram emerged as the pesticide most strongly correlated with higher cancer rates, followed by glyphosate. However, the study’s observational nature means it cannot establish a direct cause-and-effect relationship.
Picloram, developed in the 1960s and once used by the U.S. military during the Vietnam War to clear forested areas, disrupts plant hormone functions and can linger in soil for years. Its long environmental persistence raises concerns about chronic human exposure.
Other researchers are exploring additional factors behind the rise in young colorectal cancer. For example, bacterial infections during early life, such as those involving colibactin-producing microbes, may also contribute to cancer development over decades.
Cancer experts emphasize that the causes of this troubling trend are likely multifaceted, involving a combination of lifestyle, environmental, and possibly microbial factors. The American Cancer Society recently lowered the recommended age for initial colonoscopy screenings from 50 to 45 in response to the increasing incidence in younger adults.
While the new findings offer a promising lead, experts caution that further research is essential to confirm the role of picloram and to fully understand the complex web of factors influencing young-onset colorectal cancer. As Robin Mesnage, a gut microbiome researcher at King’s College London, notes, real-world exposures often involve mixtures of chemicals and contaminants, complicating efforts to pinpoint specific causes.
In the meantime, scientists continue to investigate all possible contributors, with the hope of improving prevention strategies and patient outcomes for this emerging public health challenge.