A propensity score–matched analysis of breast-conserving surgery plus whole-breast irradiation versus mastectomy in breast cancer

Purpose: Recent observations regarding long-term outcomes among patients with early-stage breast cancer (BC) who underwent breast-conserving surgery (BCS) plus whole-breast irradiation (WBI) or mastectomy are from a small number of registry-based studies. Therefore, these findings may overestimate differences in survival between the two groups, compared with randomized controlled trials conducted in the 1980s. The aim of this study is to compare long-term outcomes and clinicopathologic characteristics between patients treated with BCS + WBI or mastectomy for BC. Methods: We performed a propensity score–matched analysis in a cohort of 9710 patients aged < 70 years who underwent BCS + WBI or mastectomy without external radiotherapy for a first primary BC (pT1-2, N0-3a) at the European Institute of Oncology between 2000 and 2008. Patients were matched by propensity score. Results: Median follow-up was 8.4 years (interquartile range 6.5–10.2). The cumulative incidence of axillary lymph node recurrence at 10 years was lower in the BCS + WBI group [2.4% (95% CI, 1.7–3.3%)] than in the mastectomy group [4.4% (95% CI, 3.5–5.5%)] (P =.0005), and the cumulative incidence of contralateral BC was higher in the BCS + WBI group [3.9% (95% CI, 2.8–5.1%)] than in the mastectomy group [2.5% (95% CI, 1.7–3.4%)] (P =.01). Among the 366 patients with HER2 subtype BC, BCS + WBI was associated with a fivefold higher risk [hazard ratio 4.97 (95% CI, 2.28–10.8)] of ipsilateral breast tumor recurrence (IBTR), compared with mastectomy (P <.0001); however, among patients with other BC subtypes, the rates of IBTR were not statistically significantly different. Conclusion: Patients with HER2 subtype BC (T1-2, N0-3) who underwent BCS + WBI had a statistically significantly higher risk of IBTR than patients who underwent mastectomy. Survival was not statistically significantly different between the groups.