Comparison of Long-term Survival Outcomes of Breast Cancer in Situ Patients After Breast-Conserving Surgery with and without Radiotherapy: A Seer-based Analysis

Abstract

Background: Breast-conserving surgery (BCS) has become the most common surgical treatment for BCIS patients in the United States.Radiation therapy (RT) is recommended routinely after BCS in early stage breast cancer because it can the reduce the risk of local recurrence. However, whether radiotherapy can improve survival in BCIS remains controversial.We aimed to determine a subgroups of BCIS patients who can safely avoid RT after BCS to provide reliable evidence for clinical decision-making. Methods: Based on the SEER database, 38,829 BCIS patients who were undergone BCS between 1998 and 2019 were collected and were divided into RT group and non-RT group. Cox regression and competing risk regression were employed to estimate multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for overall survival (OS) and breast cancer–specific survival (BCSS). Subgroup analysis was performed to fifind the subgroups of people who might benefit from RT. Result: Of 38,829 eligible patients, 30,556 patients were matched. After adjustment for confounders, no statistically significant survival difference was observed between the RT group and non-RT group. Kaplan-Meier survival analysis showed that there were no significant OS (P=0.10), and BCSS (P=0.30) between RT groups and non-RT groups. After PSM, on multivariate cox regression analysis, RT did`t exert a significant influence on the OS (HR, 0.97; 95% CI [0.92, 1.03]，P=0.29) and BCSS (HR, 0.97; 95%CI [0.92, 1.03], P=0.38). Subgroup analysis results show that patients with DCIS (HR 0.92, CI [0.85, 0.99];P<0.05), poorly or worse differentiated histology(HR 0.90 , CI [0.83, 0.99];P<0.05) who received postoperative RT, achieved better OS. When the patients who tumor is larger than 5 cm (HR 0.15, CI[0.03, 0.81], P<0.05), receiving RT after BCS can obtain better BCSS. Conclusion: Radiotherapy after BCS has no effect on OS or BCSS in BCIS, but radiotherapy is also recommended for people with BCIS with poorly differentiated tumor cells and BCIS tumors larger than 5 cm. Considering these potential side effects of radiotherapy, when recommending treatment for people with BCIS, we should deliberate the necessary for radiotherapy more carefully.