Surgical Margins and Adjuvant Therapies in Malignant Phyllodes Tumors of the Breast: A Multicenter Retrospective Study.

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The optimal threshold of surgical margins for breast malignant phyllodes tumors (MPTs) and the impact of adjuvant chemotherapy and radiotherapy were investigated. We conducted a multicenter nationwide retrospective study of all MPT cases with central pathological review within the French Sarcoma Group. Endpoints were local recurrence-free survival (LRFS), metastasis-free survival (MFS), and overall survival (OS) rates. Overall, 212 patients were included in the study. All non-metastatic patients underwent primary surgical treatment, including 58.6% of conservative surgeries. An R0 resection was achieved in 117 patients (59.4%: 26.9% of patients with 1-2mm margins, 12.2% of patients with 3-7mm margins, 20.3% of patients with ≥ 8mm margins). Ninety-four patients (45%) underwent a second surgery (SS) to obtain R0 margins, with a final mastectomy rate of 72.6%. Radiotherapy and chemotherapy were performed in 91 (43.1%) and 23 patients (10.9%), respectively, but were not associated with better outcomes. Mastectomy was significantly associated with better LRFS (p < 0.001). Margins of 0, 1, or 2mm with SS were associated with better MFS (hazard ratio [HR] 0.3, p = 0.005) and OS (HR 0.32, p = 0.005) compared with margins of 0-1-2mm without SS. Wider margins (> 8mm) were not superior to margins of 3-7mm (3-7mm vs. > 8mm; HR 0.81, p = 0.69). Age (HR 2.14, p = 0.038) and tumor necrosis (HR 1.96, p = 0.047) were found to be poor prognostic factors and were associated with MFS. This study suggests that 3mm margins are necessary and sufficient for surgical management of MPTs, and emphasizes the importance of SS to obtain clear margins in case of 0-1-2mm margins. No impact of adjuvant chemotherapy or radiotherapy was detected in this study.