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 </= 55 years old, extensive intraductal component (EIC) was the next significant split. For EIC-negative tumors, age </= 35 years and negative margins were associated with a 10-year IBTR of 3%; with close (</= 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 </= 55 versus more than 55 years was the most significant factor for IBTR. Patients </= 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 </= 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.