Survival after breast-conserving surgery and radiotherapy versus mastectomy: a propensity score-matched analysis within a randomized anaesthesiology trial.

Abstract

Large, randomized studies have shown equivalent survival after breast-conserving surgery (BCS) plus adjuvant radiotherapy (RT) when compared to mastectomy. In contrast, more recent observational studies suggest BCS+RT to be superior, but it is questionable if patients in these treatment arms are comparable. Here, overall survival (OS) and breast cancer-specific survival (BCSS) after BCS+RT and mastectomy are compared within a randomized trial comparing intravenous- and inhalation anaesthesia during breast cancer (BC) surgery. The patient cohort was recruited from the randomized CAN-study. Patients with tumours larger than 30 mm, smaller than 10 mm, and those undergoing BCS without RT were excluded. OS and BCSS were estimated using multivariable Cox regression analyses and three different propensity score models. The final study cohort included 830 women, of whom 601 were treated by BCS+RT (median age 64 years) and 229 by mastectomy (median age 68 years). Women undergoing mastectomy had more comorbidities and unfavourable tumour characteristics. Mastectomy was associated with a significantly less favourable OS in unadjusted, adjusted, and propensity score matched analyses. BCSS was inferior in the mastectomy group in the unadjusted analysis with a HR 2.27 (95% CI 1.20-4.30). In the adjusted and three propensity score matched models, BCSS was equal in the treatment groups with an adjusted HR 1.02 (95% CI 0.43-2.42). In this study, which was designed to approximate a randomized trial as closely as possible, no significant difference in BCSS was observed between BCS+RT and mastectomy. Differences in OS likely reflect occult selection bias selection of patients with higher comorbidity burden to mastectomy.