Abstract PS4-11-05: Usefulness of axillary ultrasonography in selecting cases in which sentinel node biopsy can be omitted for early breast cancer

Abstract [Background] The SOUND and INSEMA trials demonstrated that the omission of sentinel lymph node biopsy (SLNB) is noninferior to axillary staging in patients with early-stage breast cancer (EBC) and negative axillary ultrasonography (AxUS). In addition, a Choosing Wisely guideline recommends omission of SLNB in low-risk elderly females with EBC. Thus, omission of SNB for EBC is on the uptrend. [Purpose] This study was conducted to identify the clinicopathological features and AxUS findings in predicting the negative sentinel nodes in our cohort. [Patients and Methods] Of the 1988 cases who underwent SNB without preoperative systemic therapy for their primary EBC from January 2016 to December 2023, 1395 cases with cT1-2N0 tumors and documented AxUS findings were included in this study. Relationships between the clinicopathological features or AxUS findings and the SNB results were evaluated. Cortical thickness greater than 2.5 mm or absence of fatty hilum and a maximum diameter greater than 1 cm were defined as findings of possible metastatic lymph nodes by AxUS. If none of these three findings were identified, the patient was defined as having no abnormal AxUS. [Result] Among 1395 cases, SN was negative in 1063 patients (76.2%). Any SLNB was positive in 332 (23.8%) patients and 83 cases (25.0%) underwent axillary dissection (ALND) and positive LN status was pN1mi(n=73,5.2%), pN1(n=213,15.3%), and >pN2(n=46, 3.3%). Older age (≥70 years), smaller clinical tumor size, and negative abnormal AxUS findings were significantly associated with SN negativity, while invasive lobular carcinoma (ILC) type was associated with SN positivity. Tumor subtypes defined by ER, PgR, and HER2 status were not associated with SN positivity. ILC type was also significantly associated ≥4 total positive lymph nodes. These findings were also true in HR+/HER2- subtypes (Table 1).When clinical tumor size was ≦1.5cm and AxUS findings were negative, SN was negative in 83.5 % and 88.2 % in all and HR+/HER2- subtype, respectively. Among these patients, moreover, in older (≥ 70) patients or patients with nuclear grade (NG)1 tumor, SN was negative in 88.2% and 92.9% in whole cohort and in 88.6% and 94.3% in HR+/HER2- subtype, respectively. [Conclusion] Older age (≥70 years), smaller clinical tumor size, and negative abnormal AxUS findings were significantly associated with SN negativity in whole cohort and HR+/HER2- subtype. This study suggests that evaluation of cortical thickness, absence of fatty hilum and maximum diameter of LNs in preoperative AxUS is very important in adapting the omission of SNB. Citation Format: W. Tajiri, Y. Nakamura, Y. Koi, S. Akiyoshi, H. Ijichi, K. Chinami, E. Tokunaga. Usefulness of axillary ultrasonography in selecting cases in which sentinel node biopsy can be omitted for early breast cancer [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 PS4-11-05.