Survival after breast conserving surgery in patients with multiple ipsilateral breast cancers.

INTRODUCTION: Breast Conserving Surgery (BCS) is the treatment of choice for unisite breast cancers. There remain concerns about the safety of BCS for multiple ipsilateral breast cancers (MIBC). The aim of this study is to determine the long-term outcomes of BCS for MIBC. METHODS: 199 patients with MIBC were treated with BCS and radiotherapy in the Edinburgh Breast Unit between 2001 and 2015. The comparison cohort included 1328 patients with unisite disease. The median follow up was greater than 10 years. In addition to analysing outcomes in the overall groups, propensity matching was performed taking account of stage, oestrogen receptor status and treatment. Outcomes were compared in matched groups of 185 unisite and MIBC patients. RESULTS: The 10-year local recurrence rate did not significantly differ between MIBC (2.8%) and unisite disease (3.1%), HR 0.82; 95%CI 0.37-1.84, p = 0.640. There was no difference in regional recurrence (HR 0.83, 95% CI 0.24-2.81, p = 0.760), distant metastases (HR, 0.75, 95% CI 0.41-1.37, p = 0.340) or breast cancer specific survival (HR 0.97, 95% CI 0.53-1.79, p = 0.930). The 10 year breast cancer specific mortality was 5.2% in MIBC and 6.2% in unisite disease. In propensity matched cohorts, MIBC was not associated with a difference in local recurrence (HR = 0.76, 95% CI 0.28-2.02, p = 0.580), regional recurrence (HR, 0.91, 95% CI 0.17-4.79, p = 0.920), distant recurrence (HR 0.62, 95% CI 0.31-1.23, p = 0.170) or breast cancer specific mortality (HR 0.84, 95% CI 0.40-1.76, p = 0.650). CONCLUSION: Unisite and MIBC have the same risk profile for local recurrence and breast cancer specific survival when treated by BCS. This study contributes to the evidence supporting the safety of BCS in MIBC.