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 20-49 years) and older adults (aged 50+ years). Design: Surveillance study Setting: 42 countries from Asia (n=11), Europe (n=22), Africa (n=1), North and South America (n=6), and Australasia (n=2) with annual cancer incidence data from 2003-2017 in the IARC Globocan database. Participants: Adults aged 20+ years. Measurements: Joinpoint regression to estimate the average annual percent change (AAPC) in cancer incidence rates for 13 cancers previously reported as increasing in multiple countries in younger adults (leukemia, breast, endometrial, colorectal, oral, kidney, liver, pancreatic, gallbladder, prostate, stomach, esophageal and thyroid cancer). Results: Cancer incidence rates increased in younger adults in most (>75%) countries between 2003-2017 for six of the 13 cancers: thyroid (median AAPC=3.57%), breast (0.89%), colorectal (1.45%), kidney (2.21%), endometrial cancer (1.66%) and leukaemia (0.78%). Incidence rates for these cancers also increased in older adults in most countries (median AAPC thyroid=3%, breast=0.86%, kidney=1.65%, endometrial=1.20% and leukemia=0.61%). The exception was colorectal cancer which only increased in older adults in around half the countries (median AAPC=0.37%), and the AAPC was greater in younger than older adults in 69% of countries. For liver, oral, oesophageal and stomach cancer, rates decreased in younger adults in more than half the countries. Limitations: Most countries with available data were high-middle income and results might not be generalizable. Conclusions: Cancer incidence rates increased for several cancers 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, clinical and public health guidelines.