The Characteristics of Local Recurrence After Breast-Conserving Surgery Alone for Malignant and Borderline Phyllodes Tumors of the Breast (KROG 16-08).

Background: Despite margin-negative breast-conserving surgery (BCS), phyllodes tumors (PT) of the breast show high local recurrence (LR) rates. In this study we aimed to assess the site and grade of LR to identify high-risk patients after initial treatment of malignant and borderline PT using BCS alone.

Patients And Methods: From 1981 to 2014, 312 patients with malignant (n = 164) and borderline (n = 148) PT were treated using BCS alone at 10 centers. LR was defined as true recurrence (TR) if < 2 cm from the primary tumor bed and as elsewhere failure (EF) if otherwise.

Results: At a median of 21 months, LR occurred in 17.6% (55 of 312), 18.9% (31 of 164) among malignant and 16.2% (24 of 148) among borderline PT (P = .636). Only 1.9% (6 of 312) had EF. Five-year cumulative LR rates were 14.7% and 35.9% after margin-negative and -positive BCS, respectively (P < .001). Positive margin was an independent risk factor for TR (P = .002) and EF (P = .002). In multivariable competing risk regression of patients with negative margins < 1 cm (n = 115), age < 35 years (P = .001), and tumor size ≥ 5 cm (P = .008) independently increased LR risk. Of patients who experienced a LR, 30.9% (17 of 55) had a second or third repeated event. Borderline-to-malignant transformation rates increased at each LR event: 4.1% (6 of 148), 12.5% (3 of 24), and 77.8% (7 of 9) at first, second, and third LR, respectively (P = .006).

Conclusion: LRs almost always develop near the primary tumor bed. Many patients experience multiple events, with heightened risk of borderline-to-malignant transformation at each subsequent event. For patients with negative margins < 1 cm, younger age and larger tumor size are independent risk factors for increased LR.