Impact of Subtype on Survival of Young Patients With Stage IV Breast Cancer

BackgroundAlthough younger age is a negative prognostic factor for patients with early stage breast cancer, data regarding the outcomes of young patients with stage IV disease are limited. We evaluated differences in overall survival (OS) according to age and disease subtype among patients with stage IV breast cancer.Patients and MethodsUsing Surveillance, Epidemiology, and End Results (SEER) data, we identified 6,302 patients aged < 60 years with de novo stage IV breast cancer between 2010 and 2014. We examined age-specific OS among hormone receptor (HR)-positive (HR⁺)/human epidermal growth factor receptor 2 (HER2)-negative (HER2⁻), HR⁺/HER2-positive (HER2⁺), HR-negative (HR⁻)/HER2⁺, and triple-negative cases using log-rank tests and Cox proportional hazards models, adjusting for relevant clinical and demographic variables.ResultsCompared with patients aged 40 to 59 years, patients aged < 40 years (n = 944; 15%) had a higher proportion of HER2⁺ cancers and a lower proportion of HR⁺/HER2⁻ disease (P < .001), but a similar proportion of triple-negative disease. Patients aged < 40 years also experienced significantly longer survival, with a median OS of 45 months (vs. 33 months). Further, after stratification by subtype, patients aged < 40 years experienced significantly longer survival, except in the setting of triple-negative disease. These survival differences persisted in adjusted analyses.ConclusionsCompared with those aged 40 to 59 years, patients with de novo metastatic breast cancer aged < 40 years experienced significantly longer survival, except in the setting of triple-negative disease. Distinct treatment-related or biological factors may exist between earlier stage and metastatic breast cancers; further examination of the potential reasons for our findings are warranted.