Postoperative Radiotherapy Contributes to the Survival Benefit of Breast-Conserving Therapy over Mastectomy

PURPOSE: A survival benefit of breast-conserving therapy (BCT) over mastectomy has been shown in recent studies. This study aimed to explore differences in recurrence patterns between BCT and mastectomy and clarify the contribution of radiotherapy (RT) to the survival benefit of BCT. METHODS: Consecutive patients with pT1-2/pN0-1/M0 breast cancer between 2009 and 2015 in our institution were retrospectively reviewed and compared in matched cohorts using 1 : 1 propensity score matching (PSM). RESULTS: A total of 2370 patients were enrolled with a median follow-up of 75 (3–148) months. In the cohort without regional nodal irradiation (RNI), WBI was associated with significantly increased 10-year relapse-free survival (RFS), distant metastasis-free survival (DMFS), and regional recurrence-free survival (RRFS) compared with mastectomy alone. There were 419 pairs in the cohort without RNI and 87 pairs in the cohort with RNI after PSM. In the PSM cohort, improved 10-year RFS (95.4% vs. 82.7%, p < 0.05), DMFS (97.4% vs. 84.1%, p < 0.05), and RRFS (99.1% vs. 95.5%, p < 0.05) were observed in WBI compared with mastectomy alone. Regarding the first recurrence event, WBI demonstrated a significantly lower cumulative rate of distant metastases than mastectomy alone. There was no significant difference in survival outcomes between WBI plus RNI and PMRT before and after the PSM. In patients without RNI, mastectomy alone was significantly associated with unfavorable RFS (HR = 2.3, 95% CI 1.2–4.5, p < 0.05) and DMFS (HR = 2.5, 95% CI 1.1–5.8, p < 0.05). CONCLUSION: This study found the benefit of RFS and DMFS in BCT patients compared with those treated with mastectomy without RNI but not in those treated with RNI. We hypothesized that RT played an important role in reducing the risk of regional recurrence and distant metastases.