Breast-conserving surgery followed by whole-breast irradiation offers survival benefits over mastectomy without irradiation

Background: The prognostic equivalence between mastectomy and breast-conserving surgery (BCS) followed by radiotherapy was shown in pivotal trials conducted decades ago. Since then, detection and treatment of breast cancer have improved substantially and recent retrospective analyses point towards a survival benefit for less extensive breast surgery. Evidence for the association of such survival data with locoregional recurrence rates is largely lacking. Methods: The Swedish Multicentre Cohort Study prospectively included clinically node-negative patients with breast cancer who had planned sentinel node biopsy between 2000 and 2004. Axillary lymph node dissection was undertaken only in patients with sentinel node metastases. For the present investigation, adjusted survival analyses were used to compare patients who underwent BCS and postoperative radiotherapy with those who received mastectomy without radiotherapy. Results: Of 3518 patients in the Swedish Multicentre Cohort Study, 2767 were included in the present analysis; 2338 had BCS with postoperative radiotherapy and 429 had mastectomy without radiotherapy. Median follow-up was 156 months. BCS followed by whole-breast irradiation was superior to mastectomy without irradiation in terms of both overall survival (79.5 versus 64.3 per cent respectively at 13 years; P < 0.001) and breast cancer-specific survival (90.5 versus 84.0 per cent at 13 years; P < 0.001). The local recurrence rate did not differ between the two groups. The axillary recurrence-free survival rate at 13 years was significantly lower after mastectomy without irradiation (98.3 versus 96.2 per cent; P < 0.001). Conclusion: The present data support the superiority or BCS with postoperative radiotherapy over mastectomy without radiotherapy. The axillary recurrence rate differed significantly, and could be one contributing factor in a complex explanatory model.