The Trade-Off of Post-Mastectomy Radiotherapy Usage for the Breast Cancer Patients Aged 70 Years or Older: A Study Based on SEER Database

Abstract Introduction: This study aimed to investigate the role of post-mastectomy radiotherapy (PMRT) in the female aged 70 years or older diagnosed with breast cancer, which is still controversial.Methods: This retrospective study enrolled women aged 70+ years diagnosed with breast cancer between 2004 and 2016 following mastectomy from the Surveillance, Epidemiology, and End Results (SEER) database. Propensity score matching (PSM) was performed to reduce covariable imbalance. A nomogram was created to predict the 1,3,5-years overall survival (OS) of elderly patients based on the the univariable and multivariable COX regression model results. The X-tile software determined the optimal cutoff value of risk scores from the nomogram and divided patients into three risk groups. Results: Of the 27,636 females were eligible, 17.2% (n=4,747) received PMRT while 82,8% (n=22889) not. After 1:1 matching, PMRT were associated with significant improvement in breast cause-specific survival (BCSS) and OS (p <0.001). By contrast, the BCSS and OS benefit from PMRT were not significant in patients with T1N1 tumor (BCSS：HR = 0.716，p = 0.249；OS：HR = 0.908，p = 0.572), and T2N1 tumor (BCSS：HR = 0.866，p = 0.289；OS：HR = 0.879，p = 0.166). Stratified by subtype, the HR+/HER-2- subtype and the HR-/HER-2- subtype (all p<0.001) have a significant prolonged survival, yet not significant difference are shown in the HER-2+ tumor. The nomogram has high predictive accuracy and discrimination, and well distinguish three risk groups. In the low-risk group, PMRT didn't significantly better OS (p=0.203).Conclusions: This study demonstrated that post-mastectomy radiotherapy improves the survival of females with elderly breast cancer. After a comprehensive assessment of the side effects and the quality of life, the omission of PMRT could be considered in patients with T1-2N1 breast cancer. Furthermore, the nomogram we constructed could be used as a decision tool for the omission of PMRT in low-risk elderly patients.