Abstract P1-14-18: Postmastectomy radiotherapy improves the outcomes of stage III breast cancer patients with negative lymph nodes after neoadjuvant chemotherapy

Abstract

Abstract Purpose: The aim of this study is to evaluate the role of postmastectomy radiotherapy (PMRT) in clinical stage II and III breast cancer patients who achieved negative node status (pN0) after neoadjuvant chemotherapy (NAC). Material and methods: We retrospectively analyzed the outcomes of 143 patients with pN0 after NAC and mastectomy at Fudan University Shanghai Cancer Center. In total, 103 (72%) patients received PMRT, and 40 (28%) patients did not. Univariate and multivariate survival analyses were performed to evaluate the effect of PMRT on locoregional recurrence-free survival (LRRFS) and overall survival (OS) of the two groups. Results: There were no differences between the two groups with respect to age, nuclear grade, estrogen receptor (ER) status, HER2/neu receptor status, lymphovascular space invasion (LVSI) status or pathological tumor size. However, a significantly higher proportion of patients in the irradiated group (64%) had clinical lymph node involvement than in the nonirradiated group (45%). After a median follow-up time of 49 months, 10 locoregional recurrence events occurred. For the entire cohort of patients, use of radiation therapy improved the 5-year LRRFS rate (94.5% vs. 80.2%; P =0.032) but not the 5-year OS rate (92.2% vs. 88.7%; P =0.617). In the subset of patients who presented with clinically stage II disease, the 5-year LRRFS and 5-year OS did not differ significantly between the PMRT and no-PMRT group (96.3% vs. 91.3%; P = 0.190 and 96.2% vs. 91.3%; P = 0.199, respectively). For patients with stage III disease at diagnosis, a trend was seen toward better local regional control with PMRT (the 5-year LRRFS rate was 92.7% vs. 64.2%; P = 0.063), although the benefit from radiation with respect to OS was not significant (5-year OS rate was 88.1% vs. 85.2%; P = 0.657). On multivariate Cox regression analyses, the clinical tumor size (hazard ratio [HR], 3.27; 95% confidence interval [CI], 1.05-10.18; P = 0.041), pathologic breast tumor response (HR, 1.82; 95% CI, 1,11-3.77; P = 0.046) and delivery of radiation therapy (HR, 1.27; 95% CI, 1.08-9.25; P = 0.047) were independent predictors of locoregional recurrence. Conclusions: For patients who achieved pN0 after NAC, PMRT seemed to provide a clinical benefit for breast cancer patients with stage III disease. Omission of PMRT in patients with stage II disease did not increase the risk of locoregional recurrence and death. Citation Format: He M, Li J, Ni X-J, Chen S, Jiang Y-Z, Di G-H, Shao Z-M. Postmastectomy radiotherapy improves the outcomes of stage III breast cancer patients with negative lymph nodes after neoadjuvant chemotherapy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-14-18.