What’s Causing Colon Cancer to Rise So Fast?

Stanfield stresses that colon cancer screening is the most effective immediate step, regardless of which environmental cause is ultimately proven. The FIT test detects hidden blood in stool, a possible sign of polyps or cancer. The USPSTF lowered the screening age from 50 to 45 in response to rising early-onset rates. Stanfield personally plans to start at 35, reflecting a more aggressive personal approach. He advises patients not to wait for symptoms, as early-stage disease is often asymptomatic. This protocol aligns with the precautionary principle: while researchers debate causes, screening can intercept the disease process early.

The Vall d'Hebron Institute of Oncology team, led by Silvana Mars and Jose Serrone, analyzed methylation patterns in 31 young-onset and 100 older colon cancers from US databases. They built scores for 14 pesticides and found picloram, a herbicide used since 1964 on rangelands and roadsides, consistently associated. The initial discovery cohort gave an odds ratio of 3, but replication in 9 independent cohorts (83 young, 272 older cases) reduced it to 1.56. The team never measured actual picloram exposure; they used methylation proxies that couldn't be validated against direct exposure data because none exists. Critics argue the proxy introduces multiple uncertainties. Further complicating the picture, German herbicide sales data show picloram was virtually absent from 1990-2005, yet Germany's early-onset colon cancer rates rose similarly to the US. This doesn't disprove the link but suggests picloram alone cannot explain the global trend. The team's molecular signal is real, but the evidence is suggestive, not definitive.

Marcos Diaz-Gay and Ludmil Alexandrov's lab at UC San Diego analyzed 981 colon cancer genomes, not initially targeting early-onset disease. They found that two specific mutational fingerprints of colibactin, a toxin from pks-positive E. coli strains, were 2.5 and 4 times more frequent in early-onset colorectal cancers compared to later-onset ones. About 21% of all colon cancers carried these signatures. Crucially, previous work from the Wellcome Sanger Institute indicates colibactin-associated mutations arise early in tumor evolution, likely within the first decade of life. The Diaz-Gay team confirmed these mutations were among the earliest drivers in the tumors. As Alexandrov starkly summarized, acquiring a driver mutation by age 10 could put someone decades ahead, leading to cancer at 40 instead of 60. Unlike the Barcelona team's correlation, this is a known mechanism: colibactin directly binds DNA, creates double-strand breaks, and leaves a specific fingerprint detectable decades later. However, the damage being done in childhood means that for a 45-year-old today, the window for prevention via targeting this bacteria may have passed, shifting focus to early-life interventions or screening.

Andrew Chan and Yin Cao's PROSPECT consortium used the Nurses' Health Study II, following 29,000 women from 1991 to 2015 with detailed food diaries and serial colonoscopies. They defined ultra-processed foods as industrially formulated items containing ingredients not typically found in home kitchens—emulsifiers, stabilizers, modified starches, packaged snacks, soft drinks, processed meats, instant meals. Comparing those consuming 10 servings/day to 3 servings/day, they observed a 45% higher risk of adenomas most likely to progress to cancer. However, this is an association, not a single-molecule mechanism. The risk could stem from emulsifiers disrupting the microbiome, low fiber, or confounding by obesity and sedentary behavior (though they adjusted for many factors). Chan himself stated diet isn't a complete explanation, noting many early-onset patients eat very healthy diets. The study's strength is its prospective design: exposure was measured directly in real people before they got sick, avoiding recall bias. It doesn't pinpoint a specific carcinogen but provides actionable direction: shift toward whole foods.

Stanfield, a doctor, advises his patients not to wait until 50 or for symptoms, and personally intends to begin FIT testing at 35. He acknowledges this is a step beyond guidelines, motivated by the alarming rise in early-onset disease. He emphasizes that screening is the single highest-impact action, and the FIT test is a non-invasive stool-based option. This personal anecdote underscores the urgency he feels and serves as a model for proactive health behavior.