A new report used data from the Global Burden of Disease 2019 study to show cancer cases in 14 to 49-year-olds rose from 1.82 million in 1990 to 3.26 million in 2019.
Based on information collected across 204 countries involving 29 cancer types, the study led by Zhejiang University School of Medicine in China also challenges common perceptions of the type of cancer that affects younger age groups.
This highlights the importance of early diagnosis and targeted treatment, the researchers argue, and that health professionals should promote a preventative lifestyle to young people, including healthy diet, tobacco and alcohol restriction, and physical activity.
New cases of early-onset cancer - defined as occurring before age 50 - are expected to increase by 31 percent worldwide by 2030, with a corresponding 21 percent increase in deaths. The risk is greatest for people aged between 40 and 49.
Over 1 million people under 50 died of cancer in 2019, with breast cancer responsible for the most deaths overall. The other dealiest cancers for younger adults in 2019 were windpipe, lung, bowel, and stomach cancers.
Breast cancer also had the highest number of cases in this age group in 2019, but windpipe (nasopharynx) and prostate cancers saw the fastest increase since 1990. On the other hand, early-onset liver cancer diagnoses declined.
Statistician Stephen Duffy from Queen Mary University of London, who was not involved in the research, suggests a potential explanation for some trends.
"In the case of liver cancer, large numbers are caused by hepatitis B virus, for which there is effective vaccination," Duffy speculates in an expert reaction to the study.
"Whereas for nasopharyngeal cancer, large numbers are caused by the Epstein-Barr virus, for which we do not have effective vaccination."
While genes play a role in some cancer cases, even in protecting against cancer, the researchers note that there are many preventable factors to consider.
"Dietary risk factors (diet high in red meat, low in fruits, high in sodium and low in milk, etc), alcohol consumption and tobacco use are the main risk factors underlying early-onset cancers," they write in their published paper.
The data also indicated inactive lifestyles, air pollution, obesity, diabetes, and high blood sugar are likely to be among the culprits.
Previous studies have found that the incidence of cancer in adults under 50 years of age has been rising since the 1990s, but most studies have focused on regional differences.
Not enough research has been done to determine the pattern of attributable risk factors for serious cancers that develop at a young age, prevalence of cancer in different socioeconomic groups, or the global disease burden.
"An important aspect of this study is the global nature of the data," Queen's University Belfast public health researchers Ashleigh Hamilton and Helen Coleman write in an editorial on the report.
"Variation across regions is demonstrated, indicating the need to understand specific risk factors for different populations."
The highest rates of early-onset cancers in 2019 were in North America, Australasia, and Western Europe, while low- to middle-income countries were affected differently, with the highest death rates in Oceania (which includes Australasia), Eastern Europe, and Central Asia. Death rates and health problems were disproportionately high in these countries, and women were particularly hard hit.
The study has some caveats, such as the fact that data quality varied across countries, underreporting was a possibility, and the effects of screening and early-life environmental factors were not made clear.
It's important to consider the data in a broader context of our growing population too, as cell biologist Dorothy Bennett from St George's, University of London, explains.
"The increase in numbers of cancer deaths in this age group was notably lower than for diagnoses, namely 28 percent," Bennett says, "which is below the increases in total population and case numbers, indicating a fall in the average cancer death rate in this group."
Cancer still kills many people despite years and years of research, so prevention is key. The evidence suggests that investing in research and educating the public and medical professionals is essential for long, healthy lives.
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