Abstract PS3-11-22: Efficacy and safety of 12-week adjuvant docetaxel plus trastuzumab in patients with node-negative HER2-positive breast cancer (tumors ≤1cm): results from the SOBER prospective single-arm trial

Abstract Background There is no standard treatment regimen for HER2-positive node-negative patients with tumor smaller than 1 cm yet. Therefore, we designed a single-arm, open, prospective, phase II study to evaluate the clinical efficacy and toxicity of adjuvant 12-week trastuzumab combined with docetaxel in HER2-positive node-negative patients with tumor smaller than 1 cm. Methods Patients having HER2-postive node-negative breast cancer with T≤1cm received docetaxel with concurrent trastuzumab for 12 weeks. The primary endpoint was 3-year disease-free survival (DFS). Th secondary endpoints included 3-year overall survival (OS) and breast cancer specific survival (BCSS). Results A total of 78 patients were enrolled in this trial. The percentage of T1mic [≤0.1 cm], T1a [>0.1 to ≤0.5 cm], and T1b [>0.5 to ≤1.0 cm]) tumors were 47.4%, 35.5% and 17.1%, respectively. After a median follow-up of 45.2 months, five DFS events were reported, with 96.9% of 3-year DFS rate and 89.8% of 5-year DFS rate. The 3-year and 5-year OS rate was 100.0% and 96.0%, respectively. No BCSS event was reported. Tumor size, molecular subtype or Ki-67 level was not associated with DFS (p>0.05) according to subgroup analyses.Fifteen (19.7%) patients had a drop in LVEF over 5% after treatment with no one having decreased LVEF over 10%. No grade 3 or 4 cardiac event was reported. The most frequently reported adverse events were neutropenia (23.7%). Conclusions Among HER2-postive node-negative breast cancer patients with T≤1cm, treatment with 12-week adjuvant docetaxel plus trastuzumab was associated with favorable prognosis and tolerable toxicity. Citation Format: S. Ding, J. Wu, D. Liu, Y. Fang, W. Wang, L. Zhu. Efficacy and safety of 12-week adjuvant docetaxel plus trastuzumab in patients with node-negative HER2-positive breast cancer (tumors ≤1cm): results from the SOBER prospective single-arm trial [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 PS3-11-22.