Early-onset breast cancer in two Brazilian tertiary cancer centers: a real-world study of years of life lost and clinical outcomes

Introduction Early-onset breast cancer (EOBC) represents a growing global concern, particularly in low- and middle-income countries, where epidemiological data remain scarce. We evaluated the clinical characteristics, temporal trends, and disease burden of EOBC in two tertiary cancer centers in São Paulo, Brazil, with a focus on Years of Life Lost (YLL) and Disability-Adjusted Life Years (DALY). Methods We conducted a retrospective study of patients diagnosed with malignant breast neoplasms between 2018 and 2023 at two tertiary cancer centers in São Paulo, Brazil. EOBC was defined as diagnosis in adult patients (aged ≥18 years) younger than 50 years. Demographics, clinical stage, and germline testing rates were compared between younger (<50) and older (≥50) patients. YLLs were calculated using individualized life expectancy estimates, and DALYs were computed as YLL + Years Lived with Disability (YLD). Group comparisons used chi-squared and Wilcoxon rank-sum tests, and multivariable logistic regression was used to evaluate factors associated with YLL >0. Results Among 3,102 patients, 43.5% were aged <50 years. EOBC patients had lower median BMI (24.6 vs. 26.1 kg/m²; p<0.001) and higher germline testing rates (21.3% vs. 11%; p<0.001). Between 2018 and 2023, the proportion of breast cancer diagnoses among patients aged <50 years varied over time, but no statistically significant temporal trend was identified (p=0.30). The distribution of non-metastatic (stages I–III) versus metastatic (stage IV) disease was similar between age groups (p=0.14). Among patients who died during follow-up, median YLL was twice as high among patients aged <50 years compared with those aged ≥50 years (42 vs. 21 years). DALY rates per 1,000 patients were 33% higher among younger patients (3,340.8 vs. 2,509.3), primarily driven by a higher rate of YLL. In multivariable analysis, treatment at the participating public institution remained associated with higher odds of YLL >0 (adjusted OR 2.15; 95% CI 1.18–3.94; p=0.013). Conclusion Within two tertiary cancer centers in São Paulo, Brazil, the proportion of EOBC diagnoses varied over the study period, without a statistically significant temporal trend. Patients aged <50 years had a greater aggregate burden of premature mortality, reflected by higher YLL and DALY rates, primarily due to the greater number of potential life years lost when death occurs at younger ages, despite a similar distribution of non-metastatic versus metastatic disease at diagnosis. These findings support the need for further research and may help inform age-specific strategies for the care of younger patients with breast cancer.