[en] Purpose: Patients with malignant phyllodes tumors of the breast (MPTB) are routinely treated with surgery alone. We performed a retrospective study to determine local control rates based on tumor size and type of surgery performed. Methods and Materials: We reviewed records of 478 patients with MPTB treated between March 1964, and August 2005. The data were extracted from the IMPAC National Oncology Database consisting of merged tumor registries from 130 hospitals. Results: Median follow-up was 64 months (range, 0-410 months). Actuarial 5-year local control rates were 79.4% for 169 lumpectomy patients and 91.2% for 207 mastectomy patients treated by surgery alone. Five-year local control rates for lumpectomy based on tumor size were 91% for 0-2 cm tumors, 85% for 2-5 cm tumors, and 59% for 5-10 cm tumors. For mastectomy patients, 5-year local control rates were 100% for 0-2 cm tumors, 95% for 2-5 cm tumors, 88% for 5-10 cm tumors, and 85% for 10-20 cm tumors. Multivariate analysis of overall survival found several factors to be significant including advancing age with each decade after 50 years of age, appearance of distant metastases, larger primary tumor size, and local control vs. local recurrence (Hazard Ratio [HR] 2.5, p < 0.05). Conclusions: Malignant phyllodes tumors of the breast local recurrence rates are 15% or greater for patients with tumors >2 cm treated by lumpectomy alone and tumors >10 cm treated by mastectomy alone. Adjuvant radiation therapy should be evaluated for these patients. This may be especially important because our study showed that local recurrence impacted on survival rates