ABSTRACT

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  stimated 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.