Real-world incidence, prevalence, and short-term outcomes in young-onset breast cancer.

Abstract

e13092 Background: Young-onset breast cancer(diagnosed at age < 40 years) is increasing in incidence,yet contemporary real-world (RW) estimates of age,race,and ethnicity stratified short-term survival remain incompletely characterized outside of population-based registries. Methods: A retrospective cohort study was conducted using the TriNetX Global Collaborative Network,an EHR platform.Female patients with incident BC(ICD-10-CM C50) diagnosed between 1/1/2015–1/1/2025 were included and stratified by age at diagnosis(18–39,40–49,50–64 years).Mortality incidence proportion was defined using all-cause mortality (“Deceased”) and further stratified by race and ethnicity.OS was evaluated over a fixed 3-year horizon to minimize bias from differential follow-up.Comparative analyses were performed using 1:1 propensity score matching (PSM) comparing age groups (18–39 vs 50–64; 40–49 vs 50–64; and 18–39 vs 40–49) with Kaplan–Meier estimation and Cox proportional hazards modeling.Sensitivity analyses included multivariable Cox proportional hazards models adjusting for comorbidities,stage,metastatic status and lines of treatment. Results: Incident cohorts included women 14,219 age18–39, 34,255 age 40–49,and 115,295 age 50–64.Mortality incidence proportion increased with age (18–39: 1.90%, 40–49: 2.16%, 50–64: 3.19%).Across all age groups, mortality incidence proportion was higher among Black vs White patients(18–39:3.40% vs 2.06%;40–49:3.70% vs 2.39%;50–64:5.16% vs 3.53%) and among non-Hispanic vs Hispanic patients (18–39:2.54% vs 1.73%;40–49: 2.45% vs 2.26%; 50–64: 3.74% vs 2.81%).In 3-year PSM analyses using ages 50–64 as the reference,all-cause mortality was lower for 18–39(HR 0.76, 95% CI 0.63–0.90;matched N = 12,327/cohort) and 40–49 (HR 0.88, 95% CI 0.78–0.98;matched N = 29,020/cohort),with no significant difference between 18–39 vs 40–49(HR 0.87, 95% CI0.72–1.04).Findings were consistent in adjusted Cox models (18–39 vs 50–64:aHR 0.78,95% CI0.68–0.89;40–49 vs 50–64:aHR 0.85, 95% CI0.78–0.93;18–39 vs 40–49:aHR 0.92, 95% CI0.79–1.07). Conclusions: In this large EHR-based cohort of incident BC,all-cause mortality increased with age and consistently differed by race and ethnicity,with higher mortality observed among Black and non-Hispanic patients across age strata.After PSM and multivariable adjustment, women diagnosed before age 50 experienced significantly lower short-term mortality risk compared with those aged 50–64.These RW findings provide updated context for age- and demographic-stratified outcomes and support targeted efforts to mitigate disparities through tailored surveillance and treatment strategies in younger BC populations. 3-year propensity score matched (PSM) overall survival. Comparison Matched N (per cohort) HR (95% CI) 18–40 vs 50–64 12,327 0.75 (0.63–0.90) 41–49 vs 50–64 29,020 0.87 (0.78–0.98) 18–40 vs 41–49 12,317 0.86 (0.71–1.04)