Abstract 675: Analysis of post mastectomy radiation outcomes in breast cancer patients with 1-3 positive axillary lymph nodes : A review of the National Cancer Database

Background: The benefit of Post mastectomy radiation (PMRT) has been confirmed in breast cancer patients with ≥4 positive axillary lymph nodes (PALN). The role of PMRT in patients with 1-3 PALN is not well defined. Methods: We identified 102,103 breast cancer patients with mastectomy and 1-3 PALN registered to the National Cancer Database (NCDB) between 2004- 2012. Primary outcome was overall survival. Adjusted variables include age, race, comorbidity, insurance, income, education, distance travelled, diagnosing/treating facility, treatment delays, hormone receptor status, regional lymph nodes, stage and treatment modalities. 8 treatment modalities were defined: +/- radiation, +/- adjuvant chemotherapy, +/- adjuvant hormone therapy. Univariate and multivariate analyses were performed to identify factors that predict overall survival. Results: Patients with 1, 2, and 3 PALN comprised 55.7%, 27.6% and 16.6% of the population, respectively. 58.4% of patients received radiation. Younger age ( $46,000, lower AJCC tumor stage, hormone receptor positive status and lower number of PALN were independently associated with a lower risk of death in multivariate analysis. Compared to patients who did not receive additional therapy, radiation alone was associated with a non-significant increased risk of death HR 1.10 (95% CI [0.92-1.31]). The addition of hormone and chemotherapy significantly reduced the risk of death HR 0.36 (95% CI [0.33- 0.3]). Stratified by regional lymph nodes, patients with 1 or 2 PALN had a trend towards increased risk of death with radiation alone compared to patients who did not receive radiation, hormone or chemotherapy. In patients with 3 PALN, there was a trend towards reduced mortality with radiation alone HR 0.89 (95% CI [0.63- 1.23]). Conclusions: To our knowledge this retrospective study is the largest such review of the outcomes of breast cancer patients with 1-3 PALN receiving adjuvant radiation following mastectomy. Our study found no measurable reduction in risk of death for those patients who received radiation therapy compared to those who did not. We also note that, with an increasing number of PALN, patients receiving PMRT either alone, or with chemotherapy or hormonal therapy, appeared to have a decrease in the risk of death compared to the populations that had not received PMRT. Based on this analysis, the routine addition of radiation following mastectomy is not indicated in patients with 1-3 PALN. The addition of adjuvant hormone and/or chemotherapy was associated with a significant survival advantage. Citation Format: Anu Paul, Runhua Shi, Prakash Peddi, Gary Burton. Analysis of post mastectomy radiation outcomes in breast cancer patients with 1-3 positive axillary lymph nodes : A review of the National Cancer Database [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 675.