The Value Of Post-mastectomy Radiotherapy In The Early Breast Cancer:A Study Based On SEER Database

Part 1The value of post-mastectomy radiotherapy for disease-specific survival in T1-2N1M0 breast cancer patientsBackground and objective:Breast cancer is the most common malignant tumor among women in developing countries and even the world.The current application of radiotherapy in breast cancer is mainly used in patients with tumors>5cm,positive lymph nodes>=4,or positive margins.These patients have a high risk of recurrence.However,there is some controversy among different researchers about whether post-mastectomy radiotherapy(PMRT)is performed in T1-2N1M0 patients.Methods:Based on the National Cancer Institute's SEER(Surveillance,Epidemiology,and End Results)database,we retrospectively analyzed the details of 181,878 primary breast cancer patients from January 2010 to December 2013.According to the inclusion and exclusion criteria,the 7466 cases were included in this study finally.They were divided into two groups according to whether they were implemented post-mastectomy radiotherapy:PMRT group and NO PMRT group.We obtained the detail clinical and pathological features of patients and analyze whether there are differences in the two groups.Simultaneously,we explored the related prognostic factors and the breast cancer-specific survival(BCSS)through the univariate and multivariate method and Kaplan-Meier method,respectively.Results:The results show that diagnosis age,year of diagnosis,marital status,T stage,number of positive lymph nodes,histological grade have relativity with PMRT.Besides,ethnicity,diagnosis age,T stage,histological grade,molecular subtype,postoperative chemotherapy,and PMRT are independent prognostic factors for BCSS.PMRT can improve patients' 5-year BCSS(p<0.001).The 5-year BCSS is 92.6%in PMRT group,however,91.0%in non-PMRT group.HR-/HER-2-type breast cancer shows the worst prognosis,in which 5-year BCSS is 75.2%.The 5-year BCSS in other types were HR-/HER-2+(90.8%),HR+/HER-2+(94.5%),and HR+/HER-2-(93.9%),respectively.Conclusion:PMRT can improve 5-year BCSS in T1-2N1M0 breast cancer patients.However,the absolute return rate is only 1.6%.There are significant differences in 5-year BCSS among four molecular subtypes of breast cancer.Part 2The effect of radiotherapy on disease-specific survival after post-mastectomy radiotherapy in different molecular classification of T1-2N1M0 breast cancer patientsBackground and objective:In the first part of this study,we confirmed that post-mastectomy radiotherapy(PMRT)can improve 5-year breast cancer-specific survival(BCSS)in T1-2N1M0 breast cancer patients and there are significant differences in 5-year BCSS among four types of breast cancer.In this part,we envisage whether the molecular classification can be used to further distinguish the degree of benefit of PMRT.Methods:We performed Kaplan-Meier survival analysis on all types of molecular classification to observe the effect of PMRT on the BCSS.Second,multi-factor analysis was performed on different molecular classifications to find out the most significant molecular type of PMRT in improving BCSS.Finally,after pairing data with PSA,we eliminate the influencing factors beyond PMRT and validates the experimental results furtherly.Results:The Kaplan-Meier analysis shows that patients with two molecular types of HR-/HER-2-and HR+/HER-2+ can obtain statistically significant benefits from PMRT(P=0.025 and 0.01,respectively).However,in multivariate analysis,PMRT can significantly improve 5-year BCSS in HR-/HER-2-(triple-negative breast cancer,TNBC)patients(P=0.029,h =1.519,95%CI:1.044-2.208).PMRT in HR+/HER-2+ patients cannot promote BCSS(P=0.833,hr=1.108,95%CI:0.429-2.857).After PSA,the PMRT still can significantly improve the 5-year BCSS among TNBC patients(P=0.025).Conclusion:In patients with T1-2N1M0,the sensitivity of different molecular types to radiotherapy is different,and TNBC type has the greatest benefit from PMRT.