Effect of breast-conserving surgery plus radiotherapy versus mastectomy on breast cancer-specific survival for early-stage contralateral breast cancer

Background: Breast-conserving surgery followed by radiotherapy is recommended in most women with early-stage unilateral breast cancer. However, its role in contralateral breast cancer (CBC) patients remains unclear. This retrospective study aimed to evaluate the breast cancer-specific survival (BCSS) outcomes after breast-conserving surgery plus radiotherapy compared with mastectomy in women with early-stage (T1- 2N0-1M0) CBC. Methods: Data were extracted from the Surveillance, Epidemiology, and End Results database. BCSS was analyzed using the log-rank method, competing risks regression model, and propensity score matching method. Results: A total of 9,336 early-stage CBC patients were included. After multivariable adjustment, no significant difference in BCSS was found between early-stage CBC patients undergoing breast-conserving surgery plus radiotherapy and those undergoing mastectomy [hazard ratio (HR) 1.11, 95% confidence interval (CI): 0.90-1.37, P=0.329]. BCSS was similar in both treatment groups and in the subgroups stratified by age at first primary breast cancer or CBC diagnosis (<= 50, 51-60, and >60 years), time interval between cancers (<0.25, 0.25-4, 5-9, and <= 10 years), stage of first primary breast cancer, T classification of CBC, histology and hormone receptors status of both cancers (all P>0.05). Among patients with N1 disease at CBC diagnosis, breast-conserving surgery plus radiotherapy was associated with a boundary significantly improved BCSS (HR 1.45, 95% CI: 1.00-2.12, P=0.050). Among patients who underwent breast-conserving surgery for first primary cancer, bilateral mastectomy for contralateral cancer did not improve BCSS compared with breast-conserving surgery plus radiotherapy (P>0.05). There was no significant difference in BCSS between breast-conserving surgery plus radiotherapy and mastectomy plus radiotherapy (P>0.05). Stable results were obtained after propensity score matching. Conclusions: Breast-conserving surgery plus radiotherapy did not significantly influence BCSS outcomes of patients with early-stage CBC. Bilateral mastectomy and mastectomy plus radiotherapy did not confer a survival advantage over breast-conserving surgery plus radiotherapy in these patients. Future prospective studies are necessary to expand on these results.