Long term outcomes of breast primary sarcomas and malignant phyllodes tumors: 20 years observational analysis of the BEAM∗ study group. (∗the breast European association for mesenchymal tumors)

Background: Primary breast sarcomas (PBS) and malignant phyllodes tumors (MPT) represent less than 1 % of breast malignancies. Current evidence relies on heterogeneous retrospective series, resulting in controversial therapeutic approaches. This study aimed to analyze long-term outcomes in a large multicentric cohort treated with consistent strategies. Materials and methods: We conducted a multicentric retrospective study involving 113 patients treated for PBS (n = 42), MPT (n = 47), and mixed cases (MC, n = 24) at 11 European breast units between 2000 and 2020. Primary endpoint was disease-free survival (DFS). Secondary endpoints included overall survival (OS), local recurrence rate (LRR), and positive margin, re-excision, and axillary involvement rates. Survival analyses were performed using the Kaplan-Meier method and log-rank test. Results: With a median follow-up of 95 months, the 10-year OS, DFS, and LRR for the entire cohort were 75.2 %, 61.9 %, and 18.4 %, respectively. Mixed cases exhibited the poorest outcomes (10-year OS: 57.6 %, DFS: 46.1 %), followed by PBS (OS: 67.5 %, DFS: 46.5 %). MPT demonstrated better survival rates (OS: 89.2 %, DFS: 82.9 %). Significant survival factors included histological subtype, surgical margins, and age. Notably, adjuvant chemotherapy was linked to worse outcomes (HR 5.11, 95 % CI 2.16–12.09, p < 0.001 for OS), likely indicating selection bias for high-risk patients. Conclusions: This study represents the largest European series with a homogeneous treatment approach and long-term follow-up. MC emerge as a distinct high-risk entity, with outcomes akin to angiosarcomas. While surgery remains the cornerstone of treatment, our data challenge the current paradigm regarding adjuvant chemotherapy, highlighting the need for new strategies, particularly for high-risk subtypes.