Cancer incidence increased worldwide between 2003 and 2017, based on registry data from 42 countries. Rates rose among adults aged 20 to 49 years as well as those aged 50 years and older, with variations by cancer type and region.
Colorectal, leukemia, thyroid, breast, kidney, and endometrial cancer incidence rose in more than three-fourths of the countries analyzed. Median annual increases among younger adults were about 4% for thyroid cancer, 2% for kidney cancer, 2% for endometrial cancer, 1% for colorectal cancer, 1% for leukemia, and 1% for breast cancer. Comparable increases occurred in older adults, though the differences between age groups were often numerically small and not statistically significant, according to findings published in Annals of Internal Medicine.
"There were relatively few countries where the magnitude of the annual change in incidence rates in younger adults was statistically significantly different from those in older adults," study researchers noted.
Colorectal cancer showed the most pronounced age difference, with faster increases among younger adults in 69% of the countries studied, a statistically significant difference in 38%. However, when multiple comparisons were accounted for, few countries showed noteworthy differences in trends.
“Our findings indicate that changes in exposures resulting in increases in incidence rates for cancer types ... are likely to be common across age groups rather than specific to cancer in younger adults since there were increases in both younger and older adults,” wrote lead author Amy Berrington de González, DPhil, of the Institute of Cancer Research, London, and colleagues.
Stomach, esophageal, liver, and oral cancers declined among younger adults in more than half of the countries, while some continued to rise in older adults. The researchers also noted that in 9 of 42 countries, joinpoint regression identified a recent decrease in thyroid cancer among younger adults, even when overall incidence rates remained positive.
The analysis included national and regional data from Asia, Europe, the Americas, Africa, and Oceania. Joinpoint regression was used to calculate the average annual percentage change in age-standardized incidence rates, allowing up to three inflection points to identify shifts in trend. The researchers compared incidence patterns between younger and older adults to detect differences across age groups and regions. The analysis was descriptive and did not assess causative factors. The study team noted that increases might reflect differences in exposure, behavior, or diagnostic activity.
Limitations included incomplete data from low-income regions, reliance on data through 2017, and potential masking of recent changes when using average annual trends. Some registries represented only regional populations rather than full national coverage.
The authors also noted that differences in screening and early detection practices may explain some of the divergent trends, particularly for colorectal cancer, where screening in older adults aids in prevention through the removal of precancerous polyps.
"Over the past several decades, there has been an insidious increase in the incidence of cancer in young adults. Furthermore, young adults appear to be at risk for presenting with more advanced stages of disease and more aggressive histologic characteristics than older patients. Although this has rightly attracted the attention of the media, advocates, and researchers, older adults continue to account for most new cancer cases and deaths worldwide,” wrote Christopher Cann, MD, of Fox Chase Cancer Center in Philadelphia, Pennsylvania, and Efrat Dotan, MD, of the University of Pennsylvania Health System, in Philadelphia, in an accompanying editorial.
Full disclosures and funding information can be found in the published study.
