Comparison of long-term results between radiotherapy after breast-conserving surgery and postmastectomy radiotherapy in stage T1-2N1M0 breast cancer

Purpose: Postoperative radiotherapy (RT) can improve survival for T1-2N1 breast cancer. However, there exists a concern whether BCS plus RT has the same or a superior therapeutic effect as that of mastectomy. In this study, we aimed to compare the long-term results between RT after BCS and postmastectomy RT in stage T1-2N1M0 breast cancer. Patients and Methods: Totally 1816 pathological stage T1-2N1M0 breast cancer patients were analyzed. The propensity score matching (PSM) method was used to select 196 pairs of patients between BCS and mastectomy receiving postoperative RT. Five-year locoregional relapse (LRR), locoregional relapse-free survival (LRFS), distant metastasis (DM), distant metastasis-free survival (DMFS), disease-free survival (DFS), breast cancer-specific survival (BCSS) were analyzed as endpoints. Results: In the whole group, significant differences were observed in all endpoints (P<0.05) between the no-RT and RT groups. For patients receiving mastectomy, DM, DMFS, DFS and BCSS rates had no differences between the two groups. For patients without RT in the multivariable analysis, the molecular subtype was associated with each endpoint (P<0.05). Age, primary tumor site, tumor size, and LVI status were significantly associated with DM. The analysis of 196 pairs of patients selected by PSM showed that BCS plus RT resulted in a significantly lower 5-year DM rate (P=0.015) and superior survival in terms of the 5-year DMFS (P=0.046), DFS (P=0.049) and BCSS (P=0.024) compared with mastectomy. Conclusions: Postoperative radiotherapy remarkably improved survival in T1-2N1M0 breast cancer but not in the mastectomy subgroup, except for LRR and LRFS. Patients with BCS plus RT had better survival compared with those with postmastectomy radiation in terms of DM, DMFS, DFS and BCSS.