Abstract 2316: Young-onset cancer incidence trends: Cohort effects on onset versus period effects on diagnosis

Background: The disproportionate increase in the diagnosis of certain cancers among younger individuals is generating intense concern. Many studies attribute the increase in so-called “young-onset” cancer to an etiologic cause but questions have also arisen about the role of earlier diagnosis. Methods: We simulate incidence trends from a natural history model that includes healthy, preclinical, and clinical disease states, where the clinical state represents diagnosis. We superimpose birth cohort effects on the rate of disease onset and period effects on the rate of transitioning to the clinical state. We examine patterns of relative incidence by age group and five-year calendar interval from 2000-2019 for six “young-onset” cancers (colon, rectum, female breast, gastric, pancreas, kidney), and identify cohort and period effects that lead to matching relative incidence patterns. Results: Two types of effects are broadly consistent with the trends in younger individuals: (1) A birth-cohort effect on disease onset that begins around 1970 and becomes more pronounced with later birth years, or (2) A progressive reduction over time in the duration of preclinical disease. An earlier, protective birth cohort effect is consistent with recent trends in incidence in older individuals that are the reverse of those in younger individuals for colon, rectal, and gastric cancers. Discussion: A disease model provides clues about the possible drivers of cancer incidence trends, suggests constraints on the patterns of exposures that might be implicated etiologically, and indicates that consideration of the role of diagnostic changes is warranted alongside potential etiologic explanations. Citation Format: Lukas Owens, Jonathan Shuhendler, Marc D. Ryser, Ruth D. Etzioni. Young-onset cancer incidence trends: Cohort effects on onset versus period effects on diagnosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2316.