# Comprehensive Clinical Characterization and Long-Term Follow-Up of the Institut Català d’Oncologia Breast Cancer Observational Cohort Study

## TL;DR

This study analyzes long-term survival and treatment patterns in breast cancer patients, especially those under 40 and over 70, using data from over 3400 patients in Spain.

## Contribution

The study provides the largest long-term observational cohort in Spain, focusing on underrepresented age groups in breast cancer research.

## Key findings

- Patients aged ≥70 had significantly lower 5- and 10-year overall survival compared to those aged 41–69.
- Age and subtype were identified as critical factors influencing survival outcomes in breast cancer patients.
- The study highlights the importance of real-world evidence for refining treatment strategies in underrepresented age groups.

## Abstract

This study examines treatment patterns and overall survival outcomes in breast cancer patients, focusing on age groups often underrepresented in clinical trials—those under 40 and over 70 years old. By analyzing data from over 3400 patients, it explores how treatment approaches and survival vary according to age and stage at diagnosis. This study provides valuable real-world evidence on long-term outcomes at 5 and 10 years, in these age extremes. The findings offer insights that may help refine treatment strategies and improve patient care, particularly for those in underrepresented age groups.

Background/Objectives: Few large cohorts with relatively uniform treatment approaches and long-term follow-up are available for assessing clinical outcomes for breast cancer (BC) patients. The Institut Català d’Oncologia (ICO) Breast Cancer Cohort was designed to well characterize treatment patterns and overall survival outcomes at 5 and 10 years, with a particular focus on patients < 40 and ≥70 years old, age groups often underrepresented in clinical trials. Methods: In this retrospective, observational study, we included all pathologically confirmed invasive BC patients diagnosed and treated between 2010 and 2014 at ICO, a Spanish reference cancer center, with a follow-up until November 2023. We collected comprehensive real-world data on clinicopathologic characteristics and treatment modalities. Overall survival (OS) was estimated using the Kaplan–Meier technique and was reported stratified by prognostic factors for the age groups of ≤40, 41–69 and ≥70. The Multivariate Cox model was used to estimate the risk of death for subgroups of age, adjusting for subtype, stage and grade. Results: Overall, 3451 patients with stage I to IV BC were diagnosed and treated, with a mean age of 58 years (range 19–98); 371 (10.8%) were diagnosed ≤40 years, and 756 (21.9%) were ≥70 years. With a mean follow-up of 9.9 years (SD = 3.5), the 5- and 10-year OS were 89% (95% CI: 86–92%) and 85% (95% CI: 81–88%) for patients ≤ 40, respectively; for those aged 41–69 years, 91% (95% CI: 90–92%) and 85% (95% CI: 83–86%), respectively; and 70% (95% CI: 66–73%) and 50% (95% CI: 47–54%) for those ≥70 years, respectively. The 5- and 10-year relative survival (RS) were 92% and 88% for patients < 70 years, respectively, and 82% and 77% for those ≥70 years, respectively. The Multivariate Cox model identified a HR of 4.90 (95% CI: 3.44–6.97, p < 0.001) for patients ≥ 70 years compared to those between 41 and 69 years. Conclusions: The ICO Breast Cancer Cohort, as far as we know, the largest in Spain with long-term follow-up, underscores the critical role of age and subtype in determining overall survival outcomes in patients with breast cancer.