Risk of Local Recurrence of Benign and Borderline Phyllodes Tumors: A Danish Population-Based Retrospective Study

To determine the recurrence rate of benign and borderline phyllodes tumors (PTs) of the breast, the association between the size of resection margin and risk of recurrence and the risk of progression of histological grading at recurrence. Nationwide retrospective study on Danish women aged 18 years or older, operated from 1999 to 2014, with resected benign or borderline PTs. Information on age, size of primary tumor and recurrence, histological grade, surgical treatment, margin size, and local recurrence were collected from the national Danish Pathology Register. A total of 479 cases were identified; 354 benign (74 %), 89 borderline (19 %), 6 uncertain histological grading (1.2 %), and 30 possibly PT (6 %). The mean age at presentation was 45.6 years (range 18-85), the mean tumor size was 3.5 cm (range 0.5-21), and the mean follow-up time was 98 months (range 1.1-192). We identified 30 local recurrences, i.e., a recurrence rate of 6.3 %. Twenty-three recurrences had similar or lower histological grading than the primary tumor, one primary benign PT recurred as a tumor with unclear diagnosis, and one primary borderline PT recurred as malignant. The number of recurrences was too low, and the information on the size of the closest resection margin was too sparse to estimate an adequate margin size for excision of nonmalignant PTs. The recurrence rate of PTs was considerably lower than previously stated in literature. No apparent pattern of progression in histological grading was found. The results do not justify wide excision margins of nonmalignant phyllodes tumors of the breast.