Malignant and borderline phyllodes tumors of the breast: a multicenter study of 362 patients (KROG 16-08).

Purpose: To identify risk factors for local recurrence (LR) and investigate roles of adjuvant local therapy for malignant and borderline phyllodes tumors of the breast.

Methods: From 1981 to 2014, 362 patients with malignant (n = 235) and borderline (n = 127) phyllodes tumors were treated by breast-conserving surgery (BCS) or total mastectomy (TM) at 10 centers. Thirty-one patients received adjuvant radiation therapy (RT), and those who received adjuvant chemotherapy were excluded from the study.

Results: Median follow-up was 5 years. LR developed in 60 (16.6%) patients. Regional recurrence occurred in 2 (0.6%) patients and distant metastasis (DM) developed in 19 (5.2%) patients. Patients receiving BCS (p = 0.025) and those not undergoing adjuvant RT (p = 0.041) showed higher LR rates. For malignant subtypes, local control (LC) rates at 5 years for BCS alone, BCS with adjuvant RT, TM alone, and TM with adjuvant RT were 80.7, 93.3, 92.4, and 100%, respectively (p = 0.033). Multivariate analyses revealed BCS alone, tumor size ≥ 5 cm, and positive margins as independent risk factors for LR. Margin-positive BCS alone showed poorest LC regardless of tumor size (62.5%, p = 0.007). For margin-negative BCS alone, 5-year LC rates for tumors ≥ 5 cm versus those < 5 cm were 71.8% versus 89.5% (p = 0.012). For borderline subtypes, only positive margins (p = 0.044) independently increased the risk of LR. DM developed exclusively in malignant subtypes and a prior LR event increased the risk of DM by sixfold (HR 6.2, 95% CI 1.6-16.1, p = 0.001).

Conclusions: Malignant and borderline phyllodes tumors with positive margins after surgery have high LR rates. After treatment by margin-negative BCS alone, patients with large malignant phyllodes tumors ≥ 5 cm also have heightened risk of LR. Thus, such patients should be considered for additional local therapy.