Influence of metastatic patterns and initial disease burden on progression- free and survival outcomes in metastatic breast cancer.

PURPOSE: The relationship between the number of initial metastases and metastatic spread in terms of progression-free survival (PFS) and overall survival (OS) in metastatic breast cancer (mBC) remains poorly understood. This study aimed to identify key factors influencing disease progression and survival from the first metastatic manifestation. METHODS: This retrospective, single center cohort study included 126 patients with breast cancer and distant metastasis treated at the University Hospital Basel, Switzerland, between 2014 and 2023. We assessed risk factors including metastatic pattern (single metastasis [SM] vs. multiple metastases [MM]), receptor status, histological subtype, and age. Disease progression from the first to second metastatic event was evaluated using the Kaplan-Meier method and log-rank test. Statistical analysis was performed using R software. RESULTS: Patients with SM exhibited significantly better PFS compared to those with MM (HR 2.11, 95% CI 1.38-3.24). Non-triple-negative breast cancer (non-TNBC) patients had superior PFS compared to those with TNBC (HR 2.61, 95% CI: 1.53-4.44). In terms of OS, SM patients had a significantly better outcome compared to MM patients (HR 2.39, 95% CI 1.43-3.99). Additionally, non-TNBC patients showed a significantly better OS than TNBC patients (HR 3.93, 95% CI: 2.2-7). CONCLUSIONS: The extent of initial metastasis and TNBC status play a crucial role in determining prognosis in mBC. These factors are essential for predicting disease progression, guiding individualized treatment strategies, and informing ongoing discussions on optimal treatment approaches for patients with oligometastatic breast cancer.