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The global incidence of early-onset cancer has increased by 79% over the last three decades, researchers reported.

In 2019, new cancer diagnoses in people under 50 totaled 3.26 million compared with 1.82 million in 1990, according to Xue Li, PhD, of Zhejiang University School of Medicine in China, and colleagues.

Meanwhile, 1.06 million people under the age of 50 died of cancer in 2019, representing a smaller increase of about 28% compared with deaths in 1990 (0.83 million), they noted in .

"Dietary risk factors, alcohol use and tobacco consumption were the main risk factors for top early-onset cancers in 2019," Li and colleagues wrote. "This study suggests that it is necessary to conduct prospective life-course cohort studies to explore the etiologies of early-onset cancers, and each country should adjust their prevention strategies based on the characteristics of early-onset cancer. Meanwhile, encouraging a healthy lifestyle could reduce early-onset cancer disease burden."

In a comment posted on , Dorothy C. Bennett, MA, PhD, of St. George's, University of London, cautioned that the increase in new cases of early-onset cancer is based on absolute numbers, rather than age-standardized rates.

"The world human population increased by 46% between 1990 and 2019, which explains part of the increase in total case numbers," she said, adding that the increase in numbers of cancer deaths in this age group (28%) was notably lower than the number of new diagnoses, "which is below the increases in total population and case numbers, indicating a fall in the average cancer death rate in this group."

Using data from the for 29 cancers in 204 countries and regions, the authors showed that early-onset breast cancer had the highest incidence rate (13.7 per 100,000) and mortality (3.5 per 100,000).

In addition, early-onset nasopharyngeal and prostate cancers showed the fastest increase in incidence, with an estimated annual percentage change (EAPC) of 2.28% (95% CI 2.1-2.47) and 2.23% (95% CI 1.97-2.49), respectively, while early-onset liver cancer showed the sharpest decline, with an EAPC of -2.88% (95% CI -3.46 to -2.3).

The early-onset cancers with the highest mortality and disability-adjusted life years were early-onset breast, tracheal, bronchus and lung, stomach, and colorectal cancers. Mortality from early-onset kidney cancer (EAPC 0.81%, 95% CI 0.70-0.92) and ovarian cancer (EAPC 0.59%, 95% CI 0.49-0.69) showed the fastest increasing trends, while mortality from early-onset liver cancer (EAPC -3.39%, 95% CI -4.00 to -2.77) showed the sharpest decline.

The results "contrast with a more traditionally held view of 'typical' cancers in adults aged under 50 years," wrote Ashleigh C. Hamilton, PhD, and Helen G. Coleman, PhD, both of Queen's University Belfast, in an . "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."

Li and colleagues also reported that the highest age-standardized incidence rates of early-onset cancer in 2019 were in North America, Australasia, and Western Europe. However, they also found disproportionately high death rates in low- to middle-income countries, with the highest age-standardized rates observed in Oceania, Eastern Europe, and Central Asia.

Age-standardized incidence and death rates of early-onset cancer will continue to increase globally from 2020 to 2030 by 31% and 21%, respectively, they said.

"Notably, the prediction model indicated that the age brackets of 40-44 and 45-49 will represent a significant proportion of the population affected by early-onset cancer morbidity and mortality in the next 10 years," they wrote.

Hamilton and Coleman noted that this "serves as a warning for future burden on healthcare systems, which are still recovering from the impact of the COVID-19 pandemic."

They also pointed out that since the results suggested that the age group most affected is 40-49, "consideration of targeted early detection measures for this age group, including the potential expansion of screening, should be considered. For example, the U.S. Preventive Services Task Force recommends that colorectal cancer screening should now begin at age 45."

Li and team acknowledged several limitations to the study, including that the accuracy of GBD data was compromised by the quality of cancer registry data in different countries.

"Thus, the under-reporting and under-diagnosis in undeveloped countries may result in underestimation of the incidences and deaths of early-onset cancer," they wrote. In addition, they suggested that the increasing trend of early-onset cancer burden "is still unclear, which may be related to early screening intervention and early-life exposures."

"Overall, there are many interesting results here," noted Stephen Duffy, MSc, of Queen Mary University of London, in another comment posted on Science Media Centre. "But they are complicated, and the cancer prevention and control community will need to take a long look at them over the next few weeks to consider exactly what they mean and what we can do to reverse some of the increasing trends."

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