Survival benefit of postoperative radiotherapy for ductal carcinoma in situ after breast-conserving surgery: a Korean population-based cohort study.

PURPOSE: It has been accepted that radiation therapy (RT) for ductal carcinoma in situ (DCIS) has no survival benefit despite increasing local control. However, a recent large database study reported a small but significant benefit. Using a Korean population-based large database, we examined the survival benefit of RT for DCIS after breast-conserving surgery (BCS) and analyzed which subgroup might derive benefit from it. METHODS: Data from 6038 female DCIS patients who underwent BCS with or without RT between 1993 and 2012 were included in this study. We used propensity score analysis to control for differences in baseline characteristics. RESULTS: Before adjusting, patients who received RT were more likely to have a large-sized tumor, poor histologic grade, poor nuclear grade, and less hormone receptor positivity. Ten-year overall survival (OS) rates were 95.0% in the non-RT group and 97.1% in the RT group (p < 0.001). After adjusting, previously noted differences of characteristics were substantially reduced, and then ten-year OS rates were 94.3% in the non-RT group and 97.6% in the RT group (p = 0.001). When examining the benefit of RT according to proposed prognostic scores, patients with a score of 0 showed no difference in OS by adding RT after BCS, whereas those with high scores demonstrated a significant benefit. CONCLUSIONS: We demonstrated the significant OS benefit of postoperative RT after BCS based on a large database, and for the first time beyond the western population. The omission of RT for selected patients to prevent overtreatment needs to be more elaborately studied.