Minimal impact of postmastectomy radiation therapy on locoregional recurrence for breast cancer patients with 1 to 3 positive lymph nodes in the modern treatment era.

INTRODUCTION: Given modern treatment strategies, controversy remains regarding whether postmastectomy radiation therapy (PMRT) is necessary for breast cancer patients with 1-3 positive axillary lymph nodes (ALN). Our aim was to assess the significance of PMRT in the modern treatment era for these patients.

MATERIAL AND METHODS: We have conducted the retrospective multicenter study and identified 658 patients with 1-3 positive ALN who were treated with mastectomy and ALN dissection between 1999 and 2012. Propensity score weighting was used to minimize the influence of confounding factors between the PMRT and no-PMRT groups. The variables including tumor size, lymph nodes status, skin and/or muscle invasion, histological grade, lymphovascular invasion and ER positivity which were statistically unbalanced between the groups were used to define the propensity scores.

RESULTS: The median follow-up time was 7.3 years. In the modern era (2006-2012), no significant difference in locoregional recurrence (LRR)-free survival was noted between the PMRT and no-PMRT groups (P = 0.3625). The 8-year LRR-free survival rates of the PMRT and no-PMRT groups were 98.2% and 95.3%, respectively. After matching patients by propensity scores, the PMRT group, compared to the no-PMRT group, exhibited significantly better locoregional control (P = 0.0366) in the entire cohort. The 10-year LRR-free survival rates were 97.8% and 88.4% in the PMRT and no-PMRT groups, respectively. In contrast, no significant difference in LRR-free survival was noted between the PMRT and no-PMRT groups in the modern era (P = 0.5298). The 8-year LRR-free survival rates of patients treated in the modern era were approximately the same between the groups (98.0% and 95.7% in the PMRT and no-PMRT groups, respectively). Particularly, LRR-free survival of HER2 positive breast cancer significantly improved in the modern treatment era, compared with that of the old treatment era (P = 0.0349).

CONCLUSION: PMRT had minimal impact on LRR for breast cancer patients with 1-3 positive ALN in the modern treatment era.