Obesity and changing Western diets are believed to be a factor (Image: Getty)
Unhealthy lifestyles, an obesity epidemic and poor gut health are feared to be fuelling a “disturbing” explosion in cases of early-onset cancer.
Analysis from Cancer Research UK suggests more adults under 50 are being struck by the disease than ever before, with younger age groups seeing the biggest rises.
Around 35,000 people aged 24 to 49 now receive the devastating news that they have cancer every year, up from 26,000 two decades ago.
Rates of cancer in that age group have surged by 24 percent since the early 1990s.
This was more than double the 10 percent increase recorded among over 75s.
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Cancer Research UK’s chief clinician, Professor Charles Swanton, described the trend as a “scientific conundrum that urgently needs to be solved”.
He said: “Evidence suggests that more adults under 50 may be getting cancer than ever before.
“You’re talking about a much younger population, often with young families. Cancer has a tremendous, often tragic impact on families.
“We are seeing them through our clinics, it is disturbing and we don’t have a good answer as to why this is happening. We’ve got to get to the bottom of it.”
The charity used the latest data to compare incidence rates in 1993-95 with 2017-19, while accounting for population changes.
Overall rates rose 13 percent from 539 to 611.5 cases per 100,000 people over that period.
The increase was 16 percent among under 24s and 14 percent among people aged 50 to 74.
Prof Swanton said young onset cancer was “still relatively uncommon” but the situation nonetheless requires investigation.
Possible factors include changes to lifestyles and diets, rising obesity levels, genetics, the microbiome and improvements in diagnosis and screening, he said.
Prof Swanton added: “There are many preventable causes of cancer we know about including smoking, obesity, red meat.
“But they don’t in themselves explain the increase we’re seeing in the under-50s.
“Bowel cancer is the one that’s the main concern. It speaks to the possibility of there being additional preventable factors that we’re not yet aware of or fully understand.”
News that the Princess of Wales, 42, had been diagnosed with cancer shocked the nation in March.
Other young victims include campaigner Dame Deborah James, who died of bowel cancer aged 40, and Girls Aloud singer Sarah Harding, who died of complications from breast cancer aged 39.
The UK is not alone in observing this alarming trend: a study led by the University of Edinburgh last year found global early-onset cases had jumped by 80 percent in 30 years.
They increased from 1.82 million in 1990 to 3.26 million in 2019, according to that study.
Prof Swanton was speaking at the American Society of Clinical Oncology’s annual conference in Chicago, where several studies added to mounting evidence that gut health is influencing the rise in younger cases.
Research from Ohio State University suggested unhealthy diets may raise risk of bowel cancer.
The balance of bacteria and inflammation in the gut may cause “accelerated ageing” in the colon, experts said.
Their analysis found that a bacteria called Fusobacterium – linked to diets low in fibre but high in sugar – increased gut inflammation, in turn raising the risk of cancer.
Under-50s with bowel cancer also had cells that appeared to be 15 years older than their real age, potentially because of damage due to long-term swelling, the researchers said.
Another possibility is that the presence of certain microbes “might initiate mutations in DNA”, Prof Swanton said, similar to how tobacco smoke induces mutations in lung cells.
He added: “Some people have suggested high fructose corn syrup, other dietary factors that are associated with obesity, or even microplastics and pollutants. We just don’t know.
“There has been an increase in obese and overweight individuals over the last 30-40 years coincident with changing Western diets. I think that may also be playing a role.”
Cancer Research UK provides funding for Cancer Grand Challenges, a scheme which invests in world-class research teams.
One team, known as PROSPECT, is racing to uncover the cause of rising global bowel cancer cases among under 50s.
Dr Lisa Wilde, director of research at Bowel Cancer UK, said: “It’s important that we see more research investment into this area of concern.”
Other results presented at the Chicago conference, from polling company Ipsos, noted an “uncharacteristic rise” in early-onset cancers in the US over the past six years.
Data from more than 385,000 patients diagnosed between January 2018 and December 2023 showed increases in tumours known to be linked to lifestyles.
The proportion of new breast cancer cases occurring among under 55s increased from 23 percent to 27 percent over the five-year period. For bowel cancer, the proportion rose from 22 percent to 17 percent.
Four in 10 cancer cases are considered preventable and Prof Swanton urged people to act to reduce their risk.
He said: “Not smoking, keeping a healthy weight, being safe in the sun and cutting down on alcohol all makes a big difference.
“Further research will help us understand the drivers of early-onset cancers so that we can prevent and detect it earlier when treatment is more likely to be successful.
“We urgently need more research to unlock the answers and understand why cancer cases are rising in younger people not only in the UK, but globally too.”