Abstract P2-11-11: Role of postmastectomy radiotherapy after neoadjuvant chemotherapy in breast cancer patients: A study from the Japanese breast cancer registry

Abstract

Abstract Background: Postmastectomy radiotherapy (PMRT) has been shown to be beneficial in node-positive breast cancer patients. However, the role of PMRT for patients receiving modern neoadjuvant chemotherapy (NAC) are controversial. We aimed to evaluate the efficacy of radiotherapy for breast cancer patients treated with NAC and mastectomy in the Japanese Breast Cancer Registry. Methods: Patients who received NAC and mastectomy for cT1-4 cN0-2 M0 breast cancer were included in this analysis. We assessed locoregional recurrence (LRR), distant disease-free survival (DDFS), and overall survival (OS) using the Kaplan-Meier method and compared them between the groups with and without PMRT by nodal status after NAC; ypN0, ypN1, and ypN2-3. We also performed multivariable cox regression analysis to evaluate the association of radiotherapy and these outcomes adjusting for baseline patient and cancer characteristics. Results: Of the 145,530 patients registered from 2004 to 2009, we identified 3,226 patients who met our inclusion criteria with the 5-year follow-up information including 1,299 ypN0, 1,036 ypN1, and 879 ypN2-3 cases. PMRT was performed in 185 patients (14.2%) with ypN0, 265 patients (25.6%) with ypN1, and 543 patients (61.8%) with ypN2-3. There was no difference in LRR, DDFS, and OS between the groups with and without radiotherapy for ypN1 patients who received NAC (P=0.72, P=0.29, and P=0.36, respectively). For patients with ypN2-3 breast cancer, radiotherapy significantly improved LRR (P<0.001), DDFS (P=0.01), and OS (P<0.001) on univariate analysis. No difference in LRR, DDFS, and OS was observed for ypN0 patients (P=0.81, P=0.15, and P=0.05, respectively). In multivariable analysis, the use of radiotherapy was independently associated with improved LRR [hazard ratio (HR): 0.608, 95% confidence interval (CI): 0.452–0.818, P=0.001] and OS [HR: 0.685, 95% CI: 0.531–0.885, P=0.004] for ypN2-3 patients. Effect of PMRT on locoregional recurrence by the ypN subgroupsypN subgroupHazard ratio95%CI Low95%CI HighP valueypN00.8550.4581.5960.623ypN10.8320.5491.2620.387ypN2-30.6080.4520.8180.001 Effect of PMRT on overall survival by the ypN subgroupsypN subgroupHazard ratio95%CI Low95%CI HighP valueypN01.3250.8412.0870.224ypN10.8800.5991.2930.514ypN2-30.6850.5310.8850.004 Radiotherapy was not associated with OS among patients with ypN0 [HR: 1.325, 95% CI: 0.841–2.087, P=0.224] and ypN1 [HR: 0.880, 95% CI: 0.599–1.293, P=0.514]. There was no significant difference in DDFS with the addition of radiotherapy for all ypN subgroups. Conclusions: The results from this nationwide database study of breast cancer patients following modern NAC showed that PMRT did not improve survival for patients with ypN1 and ypN0. Radiotherapy might be only beneficial for ypN2-3 breast cancer patients who received NAC and mastectomy in the modern era. Randomized clinical trials are needed to optimize the use of PMRT for breast cancer patients treated with neoadjuvant chemotherapy. Citation Format: Miyashita M, Niikura N, Kumamaru H, Miyata H, Ishida T, Kinoshita T, Tsuda H, Nakamura S, Tokuda Y. Role of postmastectomy radiotherapy after neoadjuvant chemotherapy in breast cancer patients: A study from the Japanese breast cancer registry [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-11-11.