Recursive partitioning identifies patients at high and low risk for ipsilateral tumor recurrence after breast-conserving surgery and radiation.

PURPOSE: Recursive partitioning analysis (RPA), a method of building decision trees of significant prognostic factors for outcome, was used to determine subgroups at significantly different risk for ipsilateral breast tumor recurrence (IBTR) in early-stage breast cancer. PATIENTS AND METHODS: Nine hundred twelve women underwent breast-conserving surgery, axillary dissection, and radiation. Systemic therapy was chemotherapy with or without tamoxifen in 32%, tamoxifen in 27%, or none in 41%. RPA was used to create a decision tree according to predictive variables that classify patients by IBTR risk, and the Kaplan-Meier method was used to calculate 10-year risks. Median follow-up was 5.9 years. RESULTS: Age was the first split in the partition tree. Patients more than 55 years old had a 4% 10-year IBTR, the only further division being use of tamoxifen or not (2% v 5%, P =.03). For patients