The association between young age at metastatic breast cancer diagnosis and overall survival in the EMBRACE study

The influence of young age at diagnosis on prognosis of patients with metastatic breast cancer (MBC) remains unclear. We examined overall survival (OS) within a single-institution prospective study of patients with de novo or recurrent MBC. Kaplan-Meier curves assessed OS by age (≤35 or ≤40 years as the youngest category) and inferred metastatic tumor subtype. Multivariable Cox regression models estimated hazard ratios (HRs) and 95% CIs for OS by age adjusting for clinical factors. Of 4189 women <75 years, 571 were ≤40 years at MBC diagnosis, of whom 260 were ≤35 years. Over half (52%) died during follow-up (median = 5.3 years, IQR = 2.1-9.8 years). Compared to patients 45-55 years, those ≤35 years at diagnosis experienced worse OS (HR = 1.22, 95%CI 1.00-1.48, p = 0.05). This association was driven by HER2-negative/luminal B-like and hormone receptor-positive/HER2-positive tumors. These findings highlight the need to develop more effective therapies for young patients with this metastatic subtype.