Trends in Cancer Incidence in Younger and Older Adults : An International Comparative Analysis.

[BACKGROUND] There is concern about widespread increases in cancer incidence rates in younger adults.

[OBJECTIVE] To compare international cancer incidence trends in younger adults (aged 20 to 49 years) and older adults (aged ≥50 years).

[DESIGN] Surveillance study.

[SETTING] Forty-two countries in Asia ( = 11), Europe ( = 22), Africa ( = 1), North and South America ( = 6), and Australasia ( = 2) with annual cancer incidence data from 2003 to 2017 in the International Agency for Research on Cancer's GLOBOCAN database.

[PARTICIPANTS] Adults aged 20 years or older.

[MEASUREMENTS] Joinpoint regression to estimate the average annual percentage change (AAPC) in cancer incidence rates for 13 cancer types previously reported to be increasing in multiple countries in younger adults (leukemia and breast, endometrial, colorectal, oral, kidney, liver, pancreatic, gallbladder, prostate, stomach, esophageal, and thyroid cancer).

[RESULTS] Incidence rates increased in younger adults in most (>75%) countries between 2003 and 2017 for 6 of the 13 cancer types: thyroid cancer (median AAPC, 3.57%), breast cancer (median AAPC, 0.89%), colorectal cancer (median AAPC, 1.45%), kidney cancer (median AAPC, 2.21%), endometrial cancer (median AAPC, 1.66%), and leukemia (median AAPC, 0.78%). Incidence rates for these cancer types also increased in older adults in most countries (median AAPCs, 3% for thyroid cancer, 0.86% for breast cancer, 1.65% for kidney cancer, 1.20% for endometrial cancer, and 0.61% for leukemia). The exception was colorectal cancer, which only increased in older adults in about half the countries (median AAPC, 0.37%), and the AAPC was greater in younger than older adults in 69% of countries. For liver, oral, esophageal, and stomach cancer, rates decreased in younger adults in more than half the countries.

[LIMITATION] Most countries with available data were high-middle-income countries, and the results might not be generalizable.

[CONCLUSION] Cancer incidence rates increased for several cancer types in many of the countries studied; however, other than colorectal cancer, these increases occurred in both younger and older adults. These findings can help inform future research and clinical and public health guidelines.

[PRIMARY FUNDING SOURCE] Institute of Cancer Research and National Institutes of Health Intramural Research Program.