Two patterns in colorectal cancer do not fit the adenoma-carcinoma sequence that screening is built on. Early-onset microsatellite-stable cancers are rising globally, and post-colonoscopy cancers occur even after high-quality guideline-concordant examinations. Meanwhile the shift toward earlier-stage diagnosis has reversed, with distal and rectal tumours rising despite being the ones screening should prevent best.
This review proposes an explanation: exposure-driven accelerated carcinogenesis. The argument is that environmental and lifestyle exposures produce subclinical inflammation, immune dysregulation, microbiome disruption and epigenetic remodelling, and that these together compress the interval from initial mutation to overt tumour — either through a short and subtle precursor phase, or directly from dysplastic mucosa with no polyp to find. The authors introduce oncoembryonic reprogramming as a candidate molecular mechanism.
This is a conceptual model, not data, and should be read as a hypothesis being put forward for testing. It is worth a clinician's attention for one practical reason: if a proportion of colorectal cancers develop too fast for a ten-year interval to catch, then interval cancers are not always a quality failure, and reassurance after a normal colonoscopy has a shorter shelf life in some patients than the interval implies.
- Take new symptoms seriously in a patient with a recent normal colonoscopy — do not let the interval override the presentation.
- Early-onset colorectal cancer is rising in India as elsewhere, and presents distally and later; age is not reassurance.
- Nothing here changes screening intervals — no data supports shortening them on this basis.
- Post-colonoscopy cancer audit remains worthwhile; this model does not excuse missed lesions, it proposes an additional mechanism alongside them.
- Rectal bleeding, changed bowel habit or iron-deficiency anaemia in a young adult deserves the same workup as in an older one.
Why it matters
It reframes interval cancer as potentially biological rather than always a failure of the examination, which changes how both are investigated.
Don't overread it
This is a proposed conceptual model with no supporting clinical data — it explains observed patterns, it does not establish the mechanism.
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