Breast-Conserving Therapy is Associated with Improved Survival Without an Increased Risk of Locoregional Recurrence Compared with Mastectomy in Both Clinically Node-Positive and Node-Negative Breast Cancer Patients.

Abstract

Randomized trials demonstrated equivalent survival between breast-conserving surgery combined with radiotherapy (BCT) and mastectomy alone. Contemporary retrospective studies using pathological stage have reported improved survival with BCT. However, pathological information is unknown before surgery. To mimic real-world surgical decision-making, this study assesses oncological outcomes by using clinical nodal status. Female patients aged 18-69 years who were treated with upfront BCT or mastectomy between 2006 and 2016 for T1-3N0-3 breast cancer were identified by using prospective, provincial database. The patients were divided into clinically node-positive (cN+) and node-negative (cN0) strata. Multivariable logistic regression was used to assess the effect of local treatment type on overall survival (OS), breast cancer-specific survival (BCSS), and locoregional recurrence (LRR). Of 13,914 patients, 8228 had BCT and 5686 had mastectomy. Mastectomy patients had higher-risk clinicopathological factors: pathologically positive axillary staging was 21% in BCT and 38% in mastectomy groups. Most patients received adjuvant systemic therapy. For cN0 patients, 7743 had BCT and 4794 had mastectomy. On multivariable analysis, BCT was associated with improved OS (hazard ratio [HR] 1.37, p<0.001) and BCSS (HR 1.32, p<0.001), whereas LRR was not different between the groups (HR 0.84, p=0.1). For cN+ patients, 485 had BCT and 892 had mastectomy. On multivariable analysis, BCT was associated with improved OS (HR 1.46, p=0.002) and BCSS (HR 1.44, p=0.008), whereas LRR was not different between the groups (HR 0.89, p=0.7). In the era of contemporary systemic therapy, BCT was associated with better survival than mastectomy, without an increased risk of locoregional recurrence for both cN0 and cN+ presentations.