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

Background: The optimal threshold of surgical margins for breast malignant phyllodes tumors (MPTs) and the impact of adjuvant chemotherapy and radiotherapy were investigated.
Patients and Methods: 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.
Results: 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 1-2 mm margins, 12.2% of patients with 3-7 mm margins, 20.3% of patients with ≥ 8 mm 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 2 mm 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 0-1-2 mm without SS. Wider margins (> 8 mm) were not superior to margins of 3-7 mm (3-7 mm vs. > 8 mm; 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.
Conclusions: This study suggests that 3 mm margins are necessary and sufficient for surgical management of MPTs, and emphasizes the importance of SS to obtain clear margins in case of 0-1-2 mm margins. No impact of adjuvant chemotherapy or radiotherapy was detected in this study.