Are there patient subsets at high locoregional failure risks after mastectomy for pT1/2 pN0 breast cancer that may warrant radiotherapy

Abstract

Postmastectomy radiotherapy (PMRT) improves locoregional control and survival in patients with tumors >5cm or node-positive disease but little information is available to guide PMRT decisions in women with T1/T2 N0 breast cancer. This study aims to identify subsets with T1/T2, N0 breast cancer at sufficiently high risks of locoregional failure (LRF) who may benefit with PMRT. Data were analyzed for 2024 women referred from 1989–1998 with pT1/T2, pN0, M0 breast cancer treated with mastectomy without adjuvant radiotherapy. Patient, tumor, and treatment factors analyzed were: age at diagnosis, tumor size, location, histology, grade, lymphovascular invasion (LVI), # nodes removed, estrogen receptor (ER) status, margin status, and systemic therapy use. Recursive partitioning analysis, a method of building decision trees using independent prognostic factors, was performed to classify subsets at different LRF risks based on combinations of prognostic factors. Median follow-up was 7.5 years. Local, regional, and combined locoregional failure rates were 4.5%, 2.7%, and 6% respectively. On multivariate analysis, independent factors predicting LRF were histologic grade (p = .001), LVI (p = .003), and T stage (p = .001). On recursive partitioning analysis, the first split in the partition tree was histologic grade. Among 1370 patients without high grade histology, LRF was 4.2%. Among 654 patients with grade III disease (LRF 10.2%), the concomitant presence of LVI (N = 168) was associated with LRF rates of 17%. In 486 patients with grade III disease without LVI, T2 tumors (N = 211) conferred LRF rates of 12%, which was increased to 20.5% among patients who did not receive systemic therapy. Women with pT1/T2 N0 breast cancer experienced high LRF rates >15% in the presence of grade III disease with LVI or T2 tumors not receiving systemic therapy. These high-risk subsets of patients with node-negative breast cancer warrant consideration of PMRT