Abstract PO3-08-12: Oncologic Safety and Preventive Impact of Nipple-Sparing Mastectomy in BRCA1/2 Mutation Carriers: A Multicenter Retrospective Study of the Korea Robot-Endoscopy Minimal Access Breast Surgery Study Group (KoREa-BSG)

Abstract Purpose: Nipple-sparing mastectomy (NSM) is known for its excellent cosmetic results and acceptable oncologic safety. However, evidence supporting NSM in breast cancer (BC) patients carrying pathogenic variant (PV) or likely pathogenic variant (LPV) in BRCA1/2 genes is still limited. This study aims to evaluate the oncologic safety of NSM in BC patients and examine its preventive effect in unaffected individuals with BRCA1/2 PV/LPV. Methods: In this multicenter, retrospective study was conducted by the Korea Robot-Endoscopic minimal access Breast Surgery study Group (KoREa-BSG). We evaluated data from women who underwent NSM and BRCA1/2 genetic testing across 19 South Korean institutions. This study included BC patients aged between 20 and 80 years who had NSM and BRCA1/2 genetic testing between January 2008 and December 2018. Patients with distant metastasis at the initial diagnosis were excluded. Results: A total of 786 women, encompassing 906 NSM cases, were included. This population comprised 120 patients who underwent bilateral NSM, 666 with unilateral NSM for unilateral BC. Among them, 214 who received neoadjuvant chemotherapy. The median follow-up period was 62 months, with an age range of 26-74 years (median 44). Sentinel lymph node biopsy was carried out in 74.7% of cases. In the bilateral NSM cohort (n=120), 36 were bilateral BC patients, 41 were unaffected carriers of BRCA1/2 PV/LPV who underwent bilateral risk-reducing NSM (RRNSM), and 33 presented with unilateral BC with BRCA1/2 PV/LPV. In the subset of 33 patients who underwent contralateral RRNSM for unilateral BC, incidental ductal carcinoma in situ (DCIS) was discovered in two cases. In comparing NSM outcomes according to BRCA status, we found no significant difference in local recurrence (LR) between BC patients with BRCA1/2 PV/LPV (n=172) and those without BRCA1/2 PV/LPV (n=592) (LR rates: 11 in BRCA1/2 PV/LPV vs. 45 in non-carriers; p = 0.7965). Of the 172 BRCA1/2 PV/LPV carriers who did not undergo RRNSM, contralateral BC occurred in 11 patients (6.4%), while no recurrence was recorded in the RRNSM group. Conclusions: NSM appears to be a feasible option in BC patients with BRCA1/2 PV/LPV. While the long-term impact of NSM on breast cancer prevention in BRCA1/2 PV/LPV carriers requires further investigation, current evidence suggests that NSM could serve as an effective risk-reducing strategy. Citation Format: Hong-Kyu Kim, Sung Yoon Jang, Soong June Bae, Eun Young Kim, Chihwan Cha, Hyung Seok Park, Jeeyeon Lee, Jun-Hee Lee, Eun-Shin Lee, Jung Eun Choi, Soo Youn Bae, Hee-Chul Shin, Dongwon Kim, Moo Hyun Lee, Yong-Yeup Kim, Sang-Ah Han, Janghee Lee, Youngwoo Chang, Junwon Min, Sanghwa Kim, Hee Jun Choi, Young-Joon Kang, Sae Byul Lee, Jai Min Ryu. Oncologic Safety and Preventive Impact of Nipple-Sparing Mastectomy in BRCA1/2 Mutation Carriers: A Multicenter Retrospective Study of the Korea Robot-Endoscopy Minimal Access Breast Surgery Study Group (KoREa-BSG) abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-08-12.