Increasing burden of early-onset cancers: disentangling the contributions of changes in risk from demographic shifts

The burden of early-onset cancers is increasing, attracting scientific and media attention. There is, however, a need to disentangle the contribution of changes in risk, that is, age-standardized rate, due to changes in carcinogenic exposure or detection practices, from the contribution of population growth and ageing, and how they differ for later-onset cancers. Using cancer registry data, we estimated these contributions in Switzerland between 1982 and 2021. A cancer was early-onset if diagnosed between ages 20-49 and later-onset if diagnosed at 50 or older. To estimate the contribution of change in risk, we computed the expected number of cases, by applying the 1982-86 (baseline) age-standardized rates to subsequent populations and calculated the difference between observed and expected cases. To estimate the contribution of population growth and ageing, we subtracted the risk contribution from the total change in observed cases since 1982-86. Between 1982-86 and 2017-21, the burden of early-onset cancers increased by 1,534 cases/year and of later-onset by 19,832. For early-onset cancers, population growth and ageing explained 71% of the increase (men: 102%; women: 58%) and changes in risk 29% (men: -2%; women: 42%). These proportions differ by cancer site, with risk contributing to a higher proportion for prostate cancer, colorectal cancer, and melanoma. For later-onset cancers, population growth and ageing explained 92% of the increase (men: 116%; women: 81%) and changes in risk 8% (men: -16%; women: 19%). Research is needed to clarify whether risk changes are due to changes in carcinogenic exposure or in detection practices.