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

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. 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. 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. 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.