A troubling rise in cancer diagnoses among young adults in England is forcing scientists to confront an unsettling question: why are people in their late teens, 20s, 30s, and 40s increasingly being affected by diseases once seen mainly in older age groups?

A major new analysis has found that 11 different cancers are becoming more common in younger people, with researchers uncovering the first strong clue behind the trend. While obesity and overweight levels appear to play a role, experts warn the explanation is far from complete, leaving a significant portion of the rise still unexplained.

Rising Cases Across 11 Cancer Types Raise Red Flags

The study, conducted by the Institute of Cancer Research and Imperial College London, shows increasing rates in thyroid, multiple myeloma, liver, kidney, gallbladder, pancreatic, womb lining (endometrial), mouth, breast, ovarian, and bowel cancers.

Bowel and breast cancers are now the most common in younger adults, accounting for a combined 11,500 cases annually, while pancreatic and gallbladder cancers remain far rarer.

Researchers noted that only bowel and ovarian cancers are rising exclusively in younger people, while the other nine are also increasing among older populations.

Despite the alarming trend, scientists emphasize that cancer in young people is still rare overall.

“Red Flag” Symptoms Missed in Tragic Case

The human cost behind the statistics is stark.

Bradley Coombes, from Portsmouth, died at just 23 from bowel cancer after months of worsening symptoms that went undiagnosed.

His mother, Caroline Mousdale, says warning signs were repeatedly overlooked because of his age.

She said he was "a really fit and healthy young man" about to sign a semi-professional football deal and was loving life. There was nothing that obviously put him at risk, she says.

After his first year at university, Bradley began losing significant weight and suffering abdominal pain, followed by diarrhoea and blood in his stools.

It took 18 months of symptoms before he was diagnosed. By then, the tumour was so large it blocked access during a colonoscopy.

Surgery and chemotherapy failed to stop the cancer’s progression, and Bradley died with his dog Buster by his side.

"I really felt, like every parent, that he would have conquered his football dreams, he would have just had a fantastic life and that's been taken away from him, because early onset bowel cancer hadn't been identified," says Caroline.

Scientists Search for Answers as Lifestyle Factors Fall Short

Researchers say it is often impossible to identify a single cause of cancer in any one individual. Instead, they examined national health and lifestyle trends to uncover broader patterns.

Smoking, alcohol consumption, physical inactivity, red and processed meat intake, and low-fibre diets have all either improved or remained stable in recent decades, making them unlikely to explain the surge.

That leaves one major factor standing out.

The report found the only lifestyle trend matching rising cancer rates is increasing overweight and obesity levels since the 1990s.

Extra fat tissue is believed to alter hormones such as insulin, which can influence cancer development.

However, the link is incomplete. In bowel cancer alone, researchers estimate that out of every 100 additional cases, only 20 may be linked to excess weight, leaving 80 cases unexplained.

“It Is Very Worrisome” Say Experts as Mystery Remains

"It is very worrisome to hear the news that cancers are increasing in young people," Prof Montserrat García Closas, from The Institute of Cancer Research, told the BBC.

"However, there are things that can be done to reduce the risk of cancer by having a healthy lifestyle - for instance, being physically active and maintaining a healthy weight."

Researchers stress that prevention still matters greatly, with nearly 40% of cancers worldwide believed to be preventable through lifestyle changes such as not smoking.

Cancer Still Rare in Young People Despite Rising Trend

Even with the increase, scientists emphasize that young people remain at far lower risk than older populations.

Around one in 1,000 people aged in their 20s, 30s, and 40s are diagnosed with cancer each year, compared with about one in 100 among those in their 50s, 60s, and 70s.

Unanswered Questions Drive New Investigations

Experts say the search for answers is far from over.

Prof Marc Gunter from Imperial College London said researchers are exploring additional possible contributors, including ultra processed foods, PFAS chemicals, antibiotic use, sweetened drinks, inflammation, air pollution, gut bacteria, and weedkillers.

He added that uncertainty remains high, noting there is "a lot we don't know".

There is also ongoing investigation into whether improved screening and earlier detection may be contributing to higher diagnosis rates in younger patients.

For now, scientists are left with a partial answer and a growing urgency to understand why cancer is increasingly striking earlier in life.