Malignant phyllodes tumors of the breast are unusual neoplasms, with an incidence of approximately 500 cases annually in the United States. Published local recurrence rates after margin-negative breast-conserving resections of borderline malignant and malignant phyllodes tumors are unacceptably high, at 24 and 20%, respectively. It is uncertain whether radiotherapy after resection of phyllodes tumors is beneficial.

We prospectively enrolled patients who were treated with a margin-negative breast-conserving resection of borderline malignant or malignant phyllodes tumors to adjuvant radiotherapy. The primary endpoint was local recurrence.

Forty-six women were treated at 30 different institutions. The mean patient age was 49 years (range, 18-76 years). Thirty patients (65%) had malignant phyllodes tumors; the rest were borderline malignant. The mean tumor diameter was 3.7 cm (range, .8-11 cm). Eighteen patients had a negative margin on the first excision. The median size of the negative margin was .35 cm (range, <.1-2 cm). Twenty-eight patients underwent a re-excision because of positive margins in the initial resection. Two patients died of metastatic phyllodes tumor. During a median follow-up of 56 months (range, 12-129 months), none of the 46 patients developed a local recurrence (local recurrence rate, 0%; 95% confidence interval, 0-8).

Margin-negative resection combined with adjuvant radiotherapy is very effective therapy for local control of borderline and malignant phyllodes tumors. The local recurrence rate with adjuvant radiotherapy was significantly less than that observed in reported patients treated with margin-negative resection alone.