Abstract PS3-08-30: Evaluation of Late Recurrence Risk in Premenopausal N0-N1 Breast Cancer Using the CTS5 Score

Abstract Background: Estrogen receptor (ER)-positive, HER2-negative breast cancer has a prolonged risk of recurrence extending up to 20 years after surgery. Extended endocrine therapy can reduce late recurrence; however, optimal selection and treatment duration remain unclear. The Clinical Treatment Score post-5 years (CTS5) is a simple tool using clinicopathological factors to estimate late recurrence risk, and this score stratifies late recurrence risk into low (3.86) groups. Although validated primarily in postmenopausal patients, CTS5’s utility in premenopausal, N0-N1 patients has not been established. This study retrospectively assessed late recurrence risk by CTS5 and evaluated the impact of extended endocrine therapy in this lower-risk population. Methods: We analyzed ER-positive, HER2-negative, non-metastatic breast cancer patients with pathological N0-1 disease treated with curative surgery between 2003-2017, excluding those with early recurrence or insufficient follow-up. CTS5 scores were calculated and categorized into risk groups, and the duration of endocrine therapy was classified as standard (7 years) or extended (≥7 years). Distant recurrence-free survival was assessed using Kaplan-Meier and Cox regression analyses to identify prognostic factors. Results: A total of 879 patients were included in this study. Median age was 45 years; 75.9% had node-negative disease and 58.5% had pathologic stage I. Adjuvant chemotherapy was administered in 30.3%, and ovarian function suppression in 27.3%. SERM was used in 76.7% of patients. The mean CTS5 score was 2.73, with 70.3% low-risk, 22.4% intermediate, and 7.1% high risk. Extended endocrine therapy ≥7 years was given to 37.7% of patients.Over a median follow-up of 8.9 years, 31 distant recurrences occurred. Eight-year distant recurrence-free survival was 99.1% (95% CI 98.2-99.9) in the low-risk group, 95.5% (92.3-98.9) in the intermediate, and 93.7% (87.1-100.0) in the high CTS5 groups (log-rank p