Age-specific relative and absolute burden of subsequent primary non-gynecologic cancers after endometrial cancer: a population-based SEER study

Purpose Standardized incidence ratios describe proportional excess but do not identify the age groups with the largest absolute burden. We compared age-specific relative, absolute-rate, and aggregate burdens of subsequent primary non-gynecologic cancers after endometrial cancer. Methods We analyzed aggregate SEER Research Data from 17 registries excluding Alaska. Women aged 20–79 years with a first malignant endometrial cancer diagnosed during 2000–2022 entered follow-up at month 12. We calculated standardized incidence ratios (SIRs), excess absolute risks (EARs), and Observed minus Expected events. Expected-offset Poisson models used HC3 covariance, with quasi-Poisson and prespecified sensitivity analyses. Results During 1,537,182 person-years, 18,239 cancers were observed and 17,576.88 were expected (SIR 1.038, 95% CI 1.023–1.053; EAR 4.31 per 10,000 person-years). Relative excess differed by age (HC3 P = 4.31×10 − 14). SIR was highest at ages 20–39 (1.328, 95% CI 1.178–1.492), whereas EAR and aggregate excess were highest at ages 40–49 (15.40 per 10,000 person-years and 302.22 events). At 120 months or longer, all-age SIR was 0.960 (95% CI 0.935–0.986). The age-by-latency interaction was not supported. Conclusion The overall excess was small, but its relative and absolute components were concentrated in adjacent younger age groups. These population-level estimates support age-specific burden reporting but not individual risk prediction or surveillance thresholds.