Emerging Cancer Incidence Trends in Canada: A Population-Based Study of the Growing Burden of Young Adult Cancers

Abstract

Background: Recent studies have identified significant increases in cancer incidence among younger adults for some cancers. We examined incidence trends of 27 cancer sites in Canada by age and birth cohort between 1983 and 2012. Methods: Canadian incidence data for 20-84 year-olds was obtained from the Cancer in Five Continents plus database. The average annual percentage change (AAPC) was calculated, and age-period-cohort modeling was used to estimate incidence rate ratios for 10-year birth cohorts. Results: Incidence significantly increased in 12 cancer sites among adults <50 years of age. The largest increases occurred for colon (AAPC20-24=4∙08, 95%CI: 2∙89 to 5∙29), gallbladder (AAPC25-29=3∙70, 95%CI=1∙27-6∙19) and anorectal (AAPC20-24=5∙25, 95%CI: 3∙50 to 7∙03) cancers. More recent birth cohorts had higher risk of these cancers compared to the 1943 reference cohort, with the risk of colon cancer more than double in the most recent cohort (IRR1988=2∙31, 95%CI=1∙62 to 3∙30) and risk of anorectal nearly five-times higher (IRR1988=4∙74, 95%CI=2∙82 to 7.97) in the most recent cohort. Incidence has decreased among younger adults for nine sites, with the largest decreases occurring for cervical (AAPC25-29 -1∙29, 95%CI: -1∙67 to -0∙90) and lung (AAPC25-29 -2∙29, 95%CI: -3∙57 to -0∙98) cancer, and melanoma (AAPC25-29 -0∙61, 95%CI: - 0∙97 to -0∙24). Decreased risks in recent birth cohorts were observed for all cancer sites with decreasing trends in younger adults. For example, the risk of lung cancer in the most recent birth cohort was less than half that of the reference cohort (IRR1988=0∙42, 95%CI=0∙23 to 0∙78). Interpretation: Incidence among young adults is increasing for cancers associated with obesity, while incidence is decreasing for cancers associated with primary prevention measures (e.g. HPV vaccination, smoking cessation campaigns). Although further studies are needed to determine other possible causes for these trends, campaigns seeking to prevent excess body weight in young adults seem warranted. Funding Statement: The authors state: No funding was associated with this manuscript. Declaration of Interests: All authors have completed the ICMJE uniform disclosure form at www.icje.org/coi_disclosure.pdf and declare: no support from any organization for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work. Ethics Approval Statement: Ethical approval was not required for this study.