Large, consistently treated breast cancer (BC) cohorts with extended monitoring remain uncommon for evaluating long-term outcomes. The Institut Català d’Oncologia (ICO) Breast Cancer Cohort was established to describe real-world treatment tendencies and 5- and 10-year overall survival, emphasizing patients younger than 40 and those aged 70 or above—groups often lacking representation in trials. This retrospective observational analysis included all individuals with histologically verified invasive BC diagnosed and treated at ICO, Spain, from 2010 to 2014, with outcome tracking until November 2023. Detailed demographic, pathologic, and therapeutic information was extracted. Overall survival (OS) was estimated through Kaplan-Meier analysis and stratified by prognostic indicators across three age brackets: ≤40, 41-69, and ≥70 years. Mortality risks were assessed with a multivariate Cox proportional hazards model controlling for tumor subtype, disease stage, and histological grade. Among 3451 women with stage I-IV BC, the average age was 58 years (range 19-98). Of these, 371 (10.8%) were ≤40 and 756 (21.9%) were ≥70. After an average 9.9-year follow-up (SD = 3.5), 5- and 10-year OS were 89% (95% CI 86-92%) and 85% (95% CI 81-88%) for patients ≤40; 91% (95% CI 90-92%) and 85% (95% CI 83-86%) for ages 41-69; and 70% (95% CI 66-73%) and 50% (95% CI 47-54%) for those ≥70. Relative survival (RS) at 5 and 10 years reached 92% and 88% for patients younger than 70, and 82% and 77% for those aged 70 or older. In the Cox model, being ≥70 years was linked to a hazard ratio (HR) of 4.90 (95% CI 3.44-6.97; p < 0.001) versus the 41-69 group. The ICO Breast Cancer Cohort—currently the largest Spanish dataset with long-term follow-up—demonstrates that both age and tumor subtype play decisive roles in shaping survival outcomes in breast cancer.
