Survival after standard or oncoplastic breast-conserving surgery versus mastectomy for breast cancer.

Background: Recent evidence suggests a survival advantage after breast-conserving surgery compared with mastectomy. Previous studies have compared survival outcomes after standard breast-conserving surgery, but no studies have compared survival outcomes after oncoplastic breast-conserving surgery. The aim of this study was to compare survival outcomes after breast-conserving surgery + radiotherapy (and an oncoplastic breast-conserving surgery + radiotherapy subgroup) with those after mastectomy ± radiotherapy.

Methods: Patients diagnosed with primary invasive breast cancer between 1 January 2010 and 31 December 2019 were identified from a prospectively maintained National Cancer Registry. Overall survival and breast cancer-specific survival outcomes were analysed using Kaplan-Meier analysis and Cox regression analysis adjusting for patient demographics, tumour characteristics, and treatment adjuncts.

Results: A total of 14 182 patients were eligible (8537 patients underwent standard breast-conserving surgery + radiotherapy, 360 patients underwent oncoplastic breast-conserving surgery + radiotherapy, 2953 patients underwent mastectomy + radiotherapy, and 2332 patients underwent mastectomy - radiotherapy). The median follow-up was 7.27 (range 0.2-13.6) years. Superior 10-year survival was observed after breast-conserving surgery + radiotherapy (overall survival: 81.2%; breast cancer-specific survival: 93.3%) compared with mastectomy + radiotherapy (overall survival: 63.4%; breast cancer-specific survival: 75.9%) and mastectomy - radiotherapy (overall survival: 63.1%; breast cancer-specific survival: 87.5%). Ten-year overall survival and breast cancer-specific survival after oncoplastic breast-conserving surgery + radiotherapy were 86.1% and 90.2% respectively. After adjusted analysis, breast-conserving surgery + radiotherapy was associated with superior survival outcomes compared with mastectomy + radiotherapy (overall survival: HR 1.34 (95% c.i. 1.20 to 1.51); breast cancer-specific survival: HR 1.62 (95% c.i. 1.38 to 1.90)) and mastectomy - radiotherapy (overall survival: HR 1.57 (95% c.i. 1.41 to 1.75); breast cancer-specific survival: HR 1.70 (95% c.i. 1.41 to 2.05)). Similar survival outcomes were observed amongst patients treated with oncoplastic breast-conserving surgery + radiotherapy compared with mastectomy + radiotherapy (overall survival: HR 1.72 (95% c.i. 1.62 to 2.55); breast cancer-specific survival: HR 1.74 (95% c.i. 1.06 to 2.86)) and mastectomy - radiotherapy (overall survival: HR 2.21 (95% c.i. 1.49 to 3.27); breast cancer-specific survival: HR 1.89 (95% c.i. 1.13 to 3.14)).

Conclusion: Breast-conserving surgery + radiotherapy and oncoplastic breast-conserving surgery + radiotherapy are associated with superior overall survival and breast cancer-specific survival compared with mastectomy ± radiotherapy. The findings should inform discussion of surgical treatment options for patients with breast cancer.