Radiation therapy following breast conserving surgery (BCS) in women with early-stage breast cancer and low oncotype scores.

Abstract

e12547 Background: Clinical trials have demonstrated radiation therapy (RT) significantly reduces local recurrence following BCS, but that omission of RT does not compromise survival in the majority of women with early stage, low risk breast cancer. Criteria for omission of RT have been based on clinical factors such as age, stage, tumor size, surgical margins and estrogen receptor (ER) status. The utility of Oncotype DX RS in determining benefit of RT is not well defined. Methods: The National Cancer Database (NCDB) was queried for women ages 50-69 with T1N0M0, grade 1-2, ER+, Her2- breast cancer who underwent BCS with negative margins and had Oncotype DX RS of 0-18. Overall survival (OS) was estimated using the Kaplan-Meier method and compared between patients who received RT and endocrine therapy (ET) versus ET alone using logrank analysis. Propensity matching was performed to reduce the impact of potential confounders and balance sample bias. Cox proportional hazards regression was used to identify predictors of OS. Results: A total of 13,648 women met inclusion criteria. The median age was 60 years. 13,389 women had adjuvant RT+ET, while 259 women had ET alone. Five year OS was 98.6% in patients who underwent RT+ET compared to 95.5% in those that had ET alone (p = 0.0012). Propensity-matching by age, Charlson Deyo Comorbid Condition score, tumor size, Oncotype RS, and race. Five year OS in the propensity matched cohort was 99.6% for women receiving RT+ET, and 98.3% for ET alone, which was not significantly different (p = 0.095). On multivariate analysis receipt of radiotherapy was not predictive of survival. Age and comorbidity score were the only significant predictors of survival. Conclusions: Patients who receive adjuvant RT with low risk, early stage ER+/Her2- breast cancer had higher OS than women who received ET alone on univariate analysis. However, results from both multivariate analysis and propensity score matching suggest no survival benefit to the addition of RT. Prospective studies are underway assessing omission of RT on the basis of multigene assays rather than clinical features alone. [Table: see text]