The number of people aged 50 and under diagnosed with cancer has risen from 1.82 million to 3.26 million in the last three decades, a surge of 79.1%, according to a study published on Wednesday.
While the international researchers behind the study said poor diet, smoking and alcohol were the major cancer risk factors in this age group, they added that "the increasing trend of early-onset cancer burden is still unclear," although some of the rise was explained by population growth.
Physical inactivity and obesity could also have contributed to the trend, the study said.
The researchers used data from the 2019 Global Burden of Disease Study, analyzing the rates of 29 different cancers in 204 countries. The study was led by the University of Edinburgh in Scotland and Zhejiang University School of Medicine in Hangzhou, China, with the United States and Sweden also participating.
What else did the study say?
The study, published in the journal BMJ Oncology, said cancer had led to the deaths of just over a million people under 50 in 2019, a rise of 28% from 1990, the study said.
The most dangerous forms were breast, windpipe, lung, bowel and stomach cancers, according to the study, with breast cancer the most commonly diagnosed in the period under consideration, 1990 to 2019.
Early onset windpipe and prostate cancers saw the fastest rise among under-50s in that period
Liver cancer cases fell by 2.9% per year.
The highest rates of cancer among under-50s were in developed countries, which could be because wealthy countries have better health care systems and catch the disease earlier, the study said.
Modelling indicates that the number of cancer cases in under 50s across the world will rise a further 31% by 2030, mostly among people aged 40-49.
In an editorial linked to the study, two doctors at Queen's University Belfast in Ireland, Ashleigh Hamilton and Helen Coleman, said it was "crucial" to work out what was driving the surge.
"Full understanding of the reasons driving the observed trends remains elusive, although lifestyle factors are likely contributing, and novel areas of research such as antibiotic usage, the gut microbiome, outdoor air pollution and early life exposures are being explored," they said.
