Background: Recent studies have identified increases in cancer incidence among younger adults for some cancers. This study examined incidence trends for 28 cancers in Canada by age and birth cohort from 1983 to 2012.
Methods: Canadian incidence data for 20 to 84 year-olds were obtained from the Cancer Incidence in Five Continents Plus database. Age-period-cohort modeling was used to estimate the average annual percentage changes (AAPCs) and incidence rate ratios (IRRs) for 10-year birth cohorts (reference cohort, 1943) for 28 cancer types.
Results: Incidence increased for 13 cancer sites among adults younger than 50 years (1983-2012), with the largest increase occurring for rectal cancer (AAPC20-24 , 5.62; 95% confidence interval [CI], 3.77-7.51) and colon cancer (AAPC20-24 , 4.08; 95% CI, 2.89-5.29). Compared with the 1943 birth cohort, persons born circa 1988 had approximately 5- and 2-fold greater risks of rectal cancer (IRR, 4.98; 95% CI, 2.87-8.63) and colon cancer (IRR, 2.31; 95% CI, 1.62-3.30), respectively. Incidence decreased among younger adults for 9 sites (1983-2012), with the largest decreases observed for lung cancer (AAPC25-29 ,-2.29; 95% CI, -3.57 to -0.98), cervical cancer (AAPC25-29 , -1.29; 95% CI, -1.67 to -0.90), and melanoma (AAPC25-29 , -0.61; 95% CI, -0.97 to -0.24). Decreased risks in recent birth cohorts were observed for all sites with decreasing trends in younger adults. For example, the risk of lung cancer was 60% lower in the 1988 birth cohort than the 1943 birth cohort (IRR, 0.42; 95% CI, 0.23-0.78).
Conclusions: Incidence among young adults is increasing for some cancers associated with obesity but decreasing for many cancers associated with infections or smoking. Although further studies are needed to replicate these findings and understand the etiology of early-onset cancers, measures to promote healthy behaviors in young adults warranted.
Keywords: Canada; cancer prevention; epidemiology; incidence; young adult cancer.
© 2020 American Cancer Society.