Abstract PS2-01-27: A retrospective cohort study on axilla management in ipsilateral breast tumor recurrence after partial mastectomy with sentinel node biopsy

Abstract Background: Sentinel node biopsy (SNB) has been the standard of care for patients with clinically node-negative breast cancer (BC) since the 2000s. Recent ASCO guidelines now permit SNB to be omitted under specific conditions in clinical T1N0 BC. While axillary lymph node dissection (ALND) remains a regional control option for early BC, optimal axillary management, including repeat SNB, for ipsilateral breast tumor recurrence (IBTR) remains undefined. To address this, the Japanese Society for Sentinel Node Navigation Surgery (SNNS), established in 1999 to advance sentinel node research in solid tumors, conducted a retrospective cohort study (UMIN No. 000049737) on axillary management in IBTR cases. Patients and Methods: We included patients with clinical Tis-4N0 BC who underwent partial mastectomy and SNB, and whose IBTR was diagnosed between January 2010 and August 2022. Exclusion criteria included clinically node-positive BC, bilateral BC, and stage IV BC. Adjuvant therapy decisions were at the physician's discretion. We analyzed clinicopathological data, focusing on lymphatic mapping and repeat SNB, from primary BC and IBTR medical records. This study received approval from the Kyorin University School of Medicine institutional review board. Results: Our study enrolled 314 eligible cases from 20 Japanese institutions. At primary BC diagnosis, 66 cases were stage 0, 178 were stage IA/B, 66 were stage IIA/B, 1 was stage IIIA, and 3 had unknown stages. SNB was successful in 312 cases (99.3%), with only 12 cases (3.8%) showing positive sentinel lymph nodes (SLN). Breast and regional nodal irradiation were performed in 237 and 8 cases, respectively. IBTR was diagnosed between 3 and 259 months (median: 70 months) after primary BC surgery. Total mastectomy was planned for 243 cases, and partial mastectomy for 64. Sixteen cases also underwent breast reconstruction. Repeat SNB was performed in 216 cases (68.7%), with successful SLN identification in 181 (83.7%). Of the 168 cases that underwent radioisotope-guided lymphatic mapping, hot spots were visualized in 112 (66.6%) via lymphoscintigraphy. SLN localization showed 175 in the ipsilateral axilla, 6 in the contralateral axilla, and 4 in the ipsilateral internal mammary lesion. Positive SLN rates were 9.1% (11 cases) for ipsilateral axilla, 1.6% (1 case) for contralateral axilla, and 0% (0 cases) for ipsilateral internal mammary lesion. Following axillary management for IBTR, repeat SNB was performed in 194 cases (61.7%), lymph node sampling in 2 (0.6%), ALND in 37 (11.7%), and no axillary surgery in 81 (25.7%). Post-IBTR axillary management, 20 cases experienced regional or contralateral lymph node recurrence, and 23 cases died. Conclusion: Repeat SNB is feasible and provides valuable information for de-escalation surgery in IBTR cases. However, axillary management should be carefully considered, taking into account both loco-regional and systemic dissemination at the time of IBTR diagnosis. Citation Format: T. Nakayama, R. Nakamura, T. Onishi, H. Yasojima, J. Ando, H. Jinno, T. Ogawa, T. Aihara, H. Matsumoto, N. Masuda, M. Kawada, S. Kuba, Y. Shinden, N. Wada, M. Kitada, M. Saito-Oba, J. Sakamoto, S. Imoto. A retrospective cohort study on axilla management in ipsilateral breast tumor recurrence after partial mastectomy with sentinel node biopsy [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-01-27.