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 less than or equal to 55 years, old, extensive intraductal component (EIC) was the next significant split. For EIC-negative tumors, age less than or equal to 35 years and negative margins were associated with a 10-year IBTR of 3%, with close (less than or equal to 2 mm) or positive margins, 34%. Patients 36 to 55 years old with estrogen receptor-positive tumors receiving tamoxifen had a risk of IBTR of 5%, but had a 20% risk without tamoxifen. Conclusion: This RPA showed that age less than or equal to 55 versus. more than 55 years was the most significant factor for IBTR. Patients less than or equal to 35 years old had a low risk of IBTR when tumors were EIC-negative with negative margins. EIC was an independent factor for IBTR for ages less than or equal to 55 years. Use of tamoxifen was the most significant factor for patients older than 55 years, but it resulted in a greater absolute decrease in risk of IBTR for patients 36 to 55 years old.