By Charlotte Webster-
Tucked away beneath the corridors of one of London’s oldest hospitals lies a treasure trove of medical history. Tens of thousands of bowel cancer tumour samples, some preserved for more than seventy years, are now at the centre of an ambitious scientific effort that may finally explain why cases of the disease are increasing among young adults.
These samples, collected long before the modern rise in early‑onset bowel cancer, offer a unique window into how the disease has changed over time. Scientists hope that by analysing them using advanced molecular techniques, they can identify patterns that reveal what is different now compared with the past.
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The unprecedented project to compare archived samples with contemporary tumours aims to give researchers clues about the root causes of this rise, potentially illuminating deep‑seated biological, environmental and lifestyle shifts that have taken place over decades.
The stored samples came from patients of all ages treated at St Mark’s Hospital, a facility whose archive of preserved tissue is believed to be unmatched anywhere in the world.
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Examining how DNA within these tumours has changed, scientists can trace what started or drove cancer development in different eras and compare that with today’s disease burden.
Understanding how bowel cancer looked in earlier decades could help narrow the field of potential causes for the growing trend among people under 50.
Researchers have already proposed a wide range of possibilities, from changes in diet and lifestyle to evolving environmental exposures and alterations in the microbial communities that live in the gut.
The archived tumour DNA acts as a historical record, containing signatures of these influences that may help scientists differentiate between what has stayed constant and what has shifted dramatically over time.
Bowel cancer, also known as colorectal cancer, remains one of the most common cancers in the UK and worldwide. Traditionally, incidence increased sharply in later life.
However, recent trends show a clear rise in cases among younger adults, a phenomenon that has alarmed health professionals and researchers alike.
Rates have increased significantly in under‑50 age groups over the last few decades, with some studies suggesting the incidence among those aged 25‑49 has risen by more than half since the early 1990s.
Large analyses also show that cancer incidence among younger adults has climbed globally, with gastrointestinal cancers including bowel cancer among the fastest‑growing categories in people under 50. While overall numbers remain lower than in older age groups, the pace of increase is rapid enough to raise concerns about future public health burdens.
Many cancers once considered diseases of older age are now being seen more frequently in those aged 30 to 39, and even in younger cohorts.
Rates in some countries have doubled or more in recent decades, while other research has shown dramatic increases in incidence among those under 40. These trends extend beyond one population or region, cropping up in Europe, North America, Oceania and elsewhere, indicating a pervasive global shift rather than a localised anomaly.
Why such a rise has occurred remains a subject of intense investigation. One leading line of inquiry focuses on the influence of microbial factors in the gut. Some strains of common bacteria, especially certain types of Escherichia coli, produce toxins that can damage DNA in bowel tissue.
There is evidence that childhood exposure to these toxins could leave genetic imprints that persist for decades, raising the risk of cancerous changes later in life. Researchers have identified mutation patterns associated with such bacterial toxins that are significantly more common in early‑onset cases than in cancers diagnosed at older ages.
Alongside microbial factors, lifestyle shifts over recent decades have also been considered potential contributors. Diets high in processed foods, rising levels of obesity, sedentary lifestyles and other changes in daily life have all been linked with a higher risk of bowel cancer.
While none of these factors provides a complete explanation, they reflect broader transformations in how young populations eat, live and interact with their environment.
The tumour archive project is adding a new dimension by allowing researchers to track molecular changes across generations. Each tumour sample holds the imprints of the exposures and biological pressures present at the time it developed.
Beyond microbial and lifestyle influences, some researchers are examining how changes in memory of other exposures such as environmental pollution, antibiotic use, food additives or even microplastics might have altered patterns of disease.
The concept of the Exposome, the totality of exposures an individual faces over their life has gained traction as scientists try to integrate genetic, environmental and behavioural data in a unified framework. Deep molecular analysis of old and new tumour samples offers one of the clearest ways to see how such factors may leave lasting imprints in the DNA of cancer cells.
At the same time, improvements in diagnostic technology and lowered screening ages have also contributed to more cancers being detected earlier in life. In some countries, screening guidelines have been lowered to include younger age groups because of the rising trend, which means that some increase in incidence reflects better detection rather than purely a true rise in occurrence.
The archived samples are now being shipped to research laboratories equipped to perform detailed genomic sequencing, microbial profiling and other analyses that were unimaginable when they were first collected decades ago.
These efforts form part of a broader international research initiative that seeks not just to document what has changed, but to understand how and why those changes have taken place.
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