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Bowel cancer in people under 50 is rising by 2 to 8 percent a year on both sides of the Atlantic and nobody knows why. The strongest lead is a toxin made by some gut bacteria whose damage signature is three times more common in young patients and is stamped on the colon early in life. If that is the cause, the fix is in childhood, not in a screening programme.
Siegel's age-period-cohort analysis of 490,305 United States cases showed that someone born around 1990 has double the colon cancer risk and quadruple the rectal cancer risk of someone born around 1950; Vuik found the same cohort pattern across 20 European countries, with incidence rising 7.9 percent a year in 20 to 29-year-olds. Neither study can say what changed. Diet, obesity, antibiotic exposure and the microbiome have all been proposed, and Hur's cohort found that each daily sugar-sweetened drink in adolescence carried a relative risk of 1.32, on 109 cases.
The 2025 genome study is the first mechanistic lead with a plausible timing. Across 981 colorectal cancer genomes from 11 countries, the colibactin signatures SBS88 and ID18 were 3.3 times more common in cancers diagnosed before 40 than after 70, were higher in countries with higher incidence, were imprinted early during tumour development and accounted for about 25 percent of APC driver indels in colibactin-positive cases. Colibactin is made by pks-positive Escherichia coli, which colonise in childhood, which would explain a birth-cohort effect that a screening programme cannot touch.
If a childhood exposure to colibactin-producing Escherichia coli writes APC mutations into the colon decades before a tumour appears, then the rise in early-onset bowel cancer may be preventable by something done in childhood rather than by screening alone.
One of the few modifiable exposures with a plausible adolescent window to match the birth-cohort pattern; it is the kind of hypothesis a cohort can generate but not settle.
The European counterpart to Siegel 2017, and the evidence a UK screening age extension has to be argued against: the fastest relative rise is in people two decades below any screening programme's start age.
The paper that turned early-onset colorectal cancer from an anecdote into a policy problem, and the direct evidence behind lowering the screening start age from 50 to 45 in the United States.
Shares Colorectal cancer incidence patterns in the United States, 1974-2013, UK gap: shorten the route to diagnosis for patients below the screening age, where the rise in incidence is, Early-onset colorectal cancer (under 50), Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood) and the tag colorectal-evidence.
Shares Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood), Prevention we already have is not deployed, The hardest cancers are found late, Colorectal cancer roadmap: from the adenoma-carcinoma sequence and the first screening trials to total mesorectal excision, oxaliplatin, RAS testing, immunotherapy for mismatch repair-deficient disease, ctDNA-guided treatment and organ preservation and the tag colorectal-evidence.
Shares APC, Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood), Prevention we already have is not deployed, The hardest cancers are found late and the tag colorectal-evidence.
Shares Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood), Prevention we already have is not deployed, The hardest cancers are found late, Colorectal cancer roadmap: from the adenoma-carcinoma sequence and the first screening trials to total mesorectal excision, oxaliplatin, RAS testing, immunotherapy for mismatch repair-deficient disease, ctDNA-guided treatment and organ preservation and the tag colorectal-evidence.
Shares Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood), Prevention we already have is not deployed, The hardest cancers are found late, Colorectal cancer roadmap: from the adenoma-carcinoma sequence and the first screening trials to total mesorectal excision, oxaliplatin, RAS testing, immunotherapy for mismatch repair-deficient disease, ctDNA-guided treatment and organ preservation and the tag colorectal-evidence.
Shares Early-onset colorectal cancer (under 50), Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood), Prevention we already have is not deployed, The hardest cancers are found late and the tag colorectal-evidence.
Shares Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood), The hardest cancers are found late, Colorectal cancer roadmap: from the adenoma-carcinoma sequence and the first screening trials to total mesorectal excision, oxaliplatin, RAS testing, immunotherapy for mismatch repair-deficient disease, ctDNA-guided treatment and organ preservation, Colorectal cancer and the tag colorectal-evidence.
Shares Colorectal cancer screening (colonoscopy, FIT, stool DNA, blood), The hardest cancers are found late, Colorectal cancer roadmap: from the adenoma-carcinoma sequence and the first screening trials to total mesorectal excision, oxaliplatin, RAS testing, immunotherapy for mismatch repair-deficient disease, ctDNA-guided treatment and organ preservation, Colorectal cancer and the tag colorectal-evidence.