Abstract PS2-04-19: 10-year survival outcomes of early-staged breast cancer patients with intermediate- and high- risk hormone receptor-positive her2-negative disease

Abstract Background: Adjuvant endocrine therapy (ET) therapy combining with CDK4/6 inhibitors have improved outcomes of early-staged breast cancer (EBC) patients (pts) with intermediate- or high- risk HR-positive HER2-negative disease based on MonarchE and NATALEE studies. The objective of this study was to assess the invasive disease-free survival (iDFS) of HR-positive HER2-negative EBC patients prior to the use of adjuvant CDK4/6 inhibitors. Methods: This is a retrospective study based on data extraction from the Hong Kong Breast Cancer Registry. Pts from 11 public and 4 private hospitals/clinics were consented for data collection. The study protocol was approved by the regional ethics committee of individual units. Pts with HR-positive HER2-negative EBC who underwent definitive surgery between January 2006 and December 2011 were studied. The inclusion criteria of NATALEE were applied. Pts were divided into two groups: group 1, those who satisfied NATALEE criteria (considered to have intermediate- or high- risk); group 2, those not eligible for NATALEE and had stage 1 cancers. Pts background characteristics were collected. iDFS was evaluated using the Kaplan-Meier method. Descriptive statistics were used to report the clinical outcomes between the two groups. Results: A total of 3512 pts were included; 1885 (53.7%) in group 1 and 1627 (46.3%) in group 2. The median age was 50.2 years (range: 24.2-101.4). 1624 (46.2%) were premenopausal, 1670 (47.6%) were postmenopausal while 218 (6.2%) had unknown menopausal status at diagnosis. 883 (25.2%) had grade 3 cancers. High tumour Ki67 (defined as >/=20%) was reported in 790 (25.2%) patients. 2459 (70.0%) received adjuvant radiotherapy, 2230 (63.5%) underwent adjuvant chemotherapy. 3341 patients received adjuvant ET (95.1%). For group 1 vs group 2, the 10-year iDFS were 77.1% vs 89.6% respectively. iDFS data according to age, menopausal status, grading, Ki-67, use of adjuvant chemotherapy and radiotherapy, are listed in Tabel 1. Conclusions: The present study confirmed that in the era prior to adjuvant ET plus CDK4/6 inhibitor, patients who had intermediate- or high- risk HR-positive HER2-negative EBC had worse prognosis. Among those who would have satisfied NATALEE criteria (group 1), older age and postmenopausal at diagnosis had significantly worse iDFS, while use of adjuvant chemotherapy was associated with better iDFS. For those with stage 1 EBC (group 2), older age and high tumour grade had significantly worse iDFS, while having receiving adjuvant radiotherapy was associated with better iDFS. Real-world studies such as the present one provide informative data and further studies may enable better determination of appropriate patient population for the use of adjuvant CDK4/6 inhibitor treatment Citation Format: W. Yeo, L. Yuen, C. Kwok, I. Soong, J. Chiu, T. Ng, S. Chan, T. Wong, C. Yolanda, L. Lawrence, C. Yau, W. Hung, C. Polly. 10-year survival outcomes of early-staged breast cancer patients with intermediate- and high- risk hormone receptor-positive her2-negative disease [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 PS2-04-19.