Patterns of metastasis and survival outcomes by age in breast cancer patients: a SEER population-based study.

Background: The role of age in metastatic disease, including breast cancer, remains obscure. This study was conducted to determine the role of age in patients with metastatic breast cancer.

Methods: Breast cancer patients diagnosed with distant metastases between 2010 and 2019 were retrieved from the Surveillance, Epidemiology, and End Results database. Comparisons were performed between young (aged ≤ 40 years), middle-aged (41-60 years), older (61-80 years), and the oldest old (> 80 years) patients. Adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) were estimated using multivariate Cox proportional hazard models. Survival analysis was performed by the Kaplan-Meier method.

Results: This study included 24155 (4.4% of all patients) metastatic breast cancer patients. The number of young, middle-aged, older, and the oldest old patients were 195 (8.3%), 9397 (38.9%), 10224 (42.3%), and 2539 (10.5%), respectively. The 5-year OS rate was highest in the young (42.1%), followed by middle-aged (34.8%), older (28.3%), and the oldest old patients (11.8%). Multivariable Cox regression analysis showed that middle-aged (aHR, 1.18; 95% CI, 1.10-1.27), older (aHR, 1.42; 95% CI, 1.32-1.52), and the oldest old patients (aHR, 2.15; 95% CI, 1.98-2.33) had worse OS than young patients. Consistently, middle-aged (aHR, 1.16; 95% CI, 1.08-1.25), older (aHR, 1.32; 95% CI, 1.23-1.43), and the oldest old patients (aHR, 1.86; 95% CI, 1.71-2.03) had worse BCSS than young patients.

Conclusion: This study provided clear evidence that metastatic breast cancer had an age-specific pattern. Age was an independent risk factor for mortality in patients with metastatic breast cancer.