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 aging, and to determine how these contributions differ for later-onset cancers. Using cancer registry data, we estimated these contributions in Switzerland between 1982 and 2021. Early-onset cancers include any cancer diagnosed in adults between 20 and 49 years, whereas later-onset cancers are those diagnosed at 50 years or older. To estimate the contribution of changes in risk, we computed the expected number of cases by applying the 1982 to 1986 (baseline) age-standardized rates to subsequent populations and calculated the difference between observed and expected cases. To estimate the contribution of population growth and aging, we subtracted the risk contribution from the total change in observed cases relative to 1982 to 1986. Between 1982 to 1986 and 2017 to 2021, the burden of early-onset cancers increased by 1,534 cases/year and that of later-onset cancers increased by 19,832. For early-onset cancers, population growth and aging explained 71% of the increase (men: 102%; women: 58%) and changes in risk explained the remaining 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 aging explained 92% of the increase (men: 116%; women: 81%) and changes in risk explained the remaining 8% (men: -16%; women: 19%). Further research is needed to clarify whether risk changes are due to changes in carcinogenic exposure or in detection practices.

Although population growth and aging are known to contribute to increasing cancer burden, their relative contribution compared with risk changes has not been quantified for early-onset cancers. Using four decades of Swiss cancer registry data, we show that demographics explain about three quarters of the increase in early-onset cases, whereas risk changes account for the remaining quarter. Contributions vary by cancer site and sex, with implications for prevention and healthcare planning.