Abstract PS2-05-12: Axillary Sentinel Lymph Node Biopsy After Neoadjuvant Chemotherapy in Clinically Node-Negative Early Breast Cancer: Feasibility and Safety in Triple-Negative and HER2-Positive Breast Cancer Subtypes

Abstract Background: Axillary sentinel lymph node biopsy (SLNB) is the standard procedure for axillary staging in patients with clinically node-negative (cN0) early breast cancer (BC). Neoadjuvant chemotherapy (NACT) achieves a pathologic complete response (pCR) in 30-50% of patients with biopsy-confirmed N1 disease. Targeted axillary dissection (TAD) has been shown to reduce false-negative rates in clinically node-positive (cN+) patients following NACT. While triple-negative breast cancer (TNBC) and HER2-positive BC exhibit high response rates to NACT (potentially leading to ypN0 status), the feasibility and safety of SLNB after NACT in cN0 patients with TNBC or HER2-positive BC remain insufficiently established by high-quality evidence. Objective: This study aimed to evaluate the feasibility of SLNB following NACT in patients with clinically node-negative TNBC and HER2-positive early BC, and to assess the oncologic safety of omitting axillary lymph node dissection (ALND) in SLNB-negative patients via long-term follow-up. Methods: A prospective single-arm trial was conducted on 404 patients with primary early breast cancer (BC, cT1b-2N0M0, age ≤70 years) who were enrolled and received neoadjuvant chemotherapy (NACT) at Peking University Cancer Hospital from October 2017 to May 2023. Inclusion criteria were: histologically confirmed invasive carcinoma, indication for chemotherapy, and eligibility for SLNB before NACT (including cases with suspicious lymph nodes but negative results on fine-needle aspiration FNA or core needle biopsy CNB). Exclusion criteria included: history of prior malignancies, contraindications to chemotherapy, prior axillary surgery, or refusal of NACT, evaluation, or study participation. Tumor subtypes were categorized as HER2-negative/hormone receptor 10% (n=147) and HER2-positive (n=242). NACT regimens were heterogeneous, including protocols such as TCbH(P) and ddEC-T±H(P). SLNB was performed using a technetium-99m-labeled tracer. Results: The success rate of SLNB was 95.63% (95% confidence interval CI: 93.60%-97.66%). Among 372 successful SLNB cases (median number of lymph nodes retrieved: 2, range: 1-10), 9 patients had positive SLNs, with a SLN-positive rate of 2.42% (95% CI: 0.86%-3.98%). Univariate analysis showed that ultrasound (US) T response, magnetic resonance imaging (MRI) T response, number of NACT cycles, Ki-67 expression level, and breast tumor pCR were factors influencing lymph node status (p 0.5). Multivariate analysis identified US T response as an independent significant factor (p=0.041). During a median follow-up of 43 months (range: 6-85 months), 1 patient developed ipsilateral axillary recurrence, with an ipsilateral axillary recurrence rate of 0.28% (95% CI: 0.05%-1.54%) among 363 SLN-negative patients who did not undergo ALND. Conclusion: SLNB following NACT in patients with clinically node-negative TNBC and HER2-positive early BC shows high success rates and low positivity rates. Omitting ALND in SLN-negative patients appears feasible, with a low risk of axillary recurrence, indicating potential oncologic safety. However, longer follow-up durations and larger-scale studies are required to validate the long-term outcomes of this approach. Citation Format: Q. Zheng, X. Wang, Y. He, W. Cao, Y. Yang, C. Gu, L. Wang, X. Wang, J. Li, T. Ouyang, Z. Fan. Axillary Sentinel Lymph Node Biopsy After Neoadjuvant Chemotherapy in Clinically Node-Negative Early Breast Cancer: Feasibility and Safety in Triple-Negative and HER2-Positive Breast Cancer Subtypes 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 PS2-05-12.