Century-old tumours could reveal why more young people are getting bowel cancer

Bowel cancer samples that have been stored for up to a century will be analysed to try to solve the mysterious rise of the disease in young people.

Despite the majority of bowel cancers still being found in older adults, the rise in younger patients has been seen around the world.

This includes in the UK where bowel cancer rates have increased by 75% in the under-24s since the early 1990s - but scientists are unclear why.

The basement at St Mark's The National Bowel Hospital has a unique collection of tens of thousands of archived cancer samples.

These are now going through advanced scientific analysis to understand what caused each cancer and what's changed over the decades.

Holly, 27, is one of a growing number of young people getting the disease.

Her bloating and weight loss were originally put down to irritable bowel syndrome until she became so ill she ended up in A&E.

The young actress was diagnosed with advanced bowel cancer and needed aggressive treatment when she was just 23.

Holly said the intense chemotherapy "affected me in ways that I never thought it would" and the "hardest thing was just accepting that… life won't be the same".

She now lives with a stoma and needs regular monitoring.

Holly has been cancer-free for more than three years and is planning her wedding, but says there are days that being diagnosed so young leaves her "screaming and crying".

"It all feels really unfair and I think, oh why me?"

Science doesn't have a clear answer either. Everything from obesity and ultra-processed foods, to antibiotics and the microbiome to air pollution and microplastics have been suggested.

"Bowel cancer in people under the age of 50 is increasing worldwide, including in the UK, and it's becoming more and more of a problem," said Dr Kevin Monahan, consultant gastroenterologist at St Mark's hospital.

"We need to develop ways that we can prevent these cancers effectively," he added.

In the UK, rates have increased by 51% in those aged 25-49 since the early 1990s although the majority of bowel cancers still occur in older adults.

Monahan said the archives contain samples from every bowel cancer patient treated at the hospital making it a "unique resource probably anywhere in the world" for uncovering causes in young people.

The bowel cancers and accompanying gut bacteria have been preserved in paraffin wax.

They are being sent to the Institute of Cancer Research (ICR) for detailed molecular analysis that has only recently become possible.

Different causes of cancer leave different marks or signatures in the DNA of the cells that have become cancerous.

Tracking how common different signatures are over time would point to the likely cause of cancer in young people.

Prof Trevor Graham, from the ICR, said: "Our leading idea is that there's a particular kind of E. coli that lives in the bowels of young people today that wasn't there in the past."

It is thought these bacteria are releasing toxins that damage the DNA inside bowel tissue, turning it cancerous. Although it asks the question why are these bacteria more common now?

"If these so-called bad bugs are causing the increase, we should see the signature of these bad bugs, the damage, was rare in the past and becomes increasingly common as we move towards the present day... we can also test other ideas too," said Graham.

But whatever is behind the increase, he said the archives are a "real treasure trove" adding: "I think the answer might be in this room."