Abstract P1-10-07: Role of postmastectomy radiation therapy in breast cancer patients according to pathologic nodal status after neoadjuvant chemotherapy

Abstract

Abstract Purpose: The role of post-mastectomy radiation therapy (PMRT) in breast cancer patients after neoadjuvant chemotherapy (NAC) is highly controversial. This study aimed to evaluate the impact of PMRT according to pathologic nodal status. Methods and Materials: We retrospectively reviewed 682 patients with clinical stage II-III breast cancer who underwent NAC and mastectomy from 2013 to 2017. Of total, 596 (87.4%) received PMRT and 86 (12.6%) did not. We investigated the relationship amongst locoregional recurrence-free survival (LRRFS), disease-free survival (DFS), overall survival (OS), and various prognostic factors. Subgroup analyses to identify the patients who may benefit from PMRT were also performed. Results: The median follow-up duration was 67 months. In ypN+ patients (n = 368, 51.2%), PMRT showed significant benefit for LRRFS, DFS, and OS (all p < 0.001). Based on multivariate analysis, histologic grade (HG) III (hazard ratio [HR] = 3.67, p = 0.002), lymphovascular invasion (LVI) (HR = 2.38, p = 0.045), and ypN2-3 (HR = 2.37, p = 0.02) were identified as significant risk factors for poor LRRFS. In ypN1 patients with more than two factors among (i) luminal subtype (ii) HG I-II and (iii) absence of LVI, PMRT showed no significant difference in LRRFS (p = 0.18). In ypN0 patients (n = 351, 48.8%), PMRT was not significantly associated with LRRFS, DFS, and OS. However, PMRT showed better LRRFS in triple-negative breast cancer (TNBC) subtype (p = 0.04). Conclusion: PMRT had a high impact on treatment outcomes in patients with residual lymph nodes following NAC and mastectomy. Among the ypN0 patients, PMRT may be beneficial only in the TNBC subtype. Citation Format: Dowook Kim, Jin Ho Kim, In Ah Kim, Ji Hyun Chang, Kyung Hwan Shin. Role of postmastectomy radiation therapy in breast cancer patients according to pathologic nodal status after neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-07.