A major analysis by the World Cancer Research Fund (WCRF) found significant increases in early-onset cancer rates for seven cancer types in England, five in the United States and four in the Netherlands.
The findings come as cancer rates continue to increase globally, with the rise among people under 50 occurring more rapidly than in older age groups.
In England, prostate cancer among men under 50 increased from one case per 100,000 people in 2001 to 3.6 cases per 100,000 in 2023.
Over the same period, bowel cancer among people under 50 rose from 3.9 cases per 100,000 to 8.4, while early-onset uterine and kidney cancers doubled to 3.9 and 3 cases per 100,000 respectively.
Breast cancer among younger adults also increased, although less sharply, rising from 42 cases per 100,000 to 47.5 in 2023.
The study also found increases in early-onset pancreatic and liver cancers in England.
In the United States, official data dating from 2000 showed that kidney cancer among people under 50 more than doubled, rising from 2.5 cases per 100,000 people in 2000 to 5.3 in 2023.
Bowel, uterine and pancreatic cancers each increased by more than 50% among younger Americans, while breast cancer rose by about 20%.
In the Netherlands, researchers identified significant increases in early-onset bowel, kidney, liver and cervical cancers.
By contrast, lung cancer rates among people under 50 declined in all three countries, a trend researchers linked to continuing declines in smoking.
Mark Lawler, professor of digital health and the chair in translational cancer genomics at Queen’s University Belfast, described the trend as “a ticking timebomb that we need to diffuse as quickly as possible, otherwise the numbers will undoubtedly continue to grow”.
He added: “The overall trend is also particularly worrying as it comes on the backdrop of lifestyle factors contributing to thousands of deaths.”
The WCRF said the growing prevalence of obesity, poor diets, insufficient physical activity, alcohol consumption, smoking and environmental exposures, including pollutants, chemicals, plastics and air and water pollution, could be contributing to the increase.
The organization estimates that about 40% of cancers are linked to modifiable risk factors.
At the same time, researchers cautioned that greater awareness of cancer symptoms and improvements in early detection could also be contributing to the higher recorded incidence among younger people.
Cancer remains substantially more common among older adults, with the median age at diagnosis above 60.
Dr Giota Mitrou, the executive director of research and policy at the WCRF, called the trajectory “concerning”.
“Behind every figure is a person facing cancer earlier than they, their family and often their doctor would expect,” Mitrou said.
“While cancer is still much more common in older adults, these changing patterns among younger generations need to be treated as a serious research and cancer prevention priority.”
The researchers said the findings underline the need for further research into the causes of rising early-onset cancer rates and greater emphasis on cancer prevention as the burden increasingly affects younger generations.