Abstract PO5-01-12: Factors Influencing Late Recurrence in Breast Cancer: A Comprehensive Analysis of the Impact of Hormone Therapy Regimens

Abstract Late recurrence of breast cancer remains a significant challenge in patient management. Despite the established efficacy of hormone therapy, factors influencing late recurrence and the impact of different hormone therapy regimens on this outcome are not yet fully understood. This study aims to investigate the key determinants contributing to late recurrence within the context of different hormone therapy regimens. This study is a retrospective analysis of medical records from two institutions between 1988 and 2018, specifically examining patients who had HR-receptor positive breast cancer who underwent surgery and completed a 5-year course of standard hormone therapy. Primary endpoint is to identify the demographic, clinical and pathologic factors as associated with late recurrence. Out of 1929 eligible patients, 49.6% (956) received Tamoxifen (TMX), 37.6% (726) received Aromatase inhibitors (AI), and 12.8% (247) switched between regimens (TMX to AI or AI to TMX). Median follow-up was 12.1 years (3.75 - 21.41 years). During this period, all-type recurrence (ATR) occurred in 9.3% of all patients, with higher rates in the TMX recipients (12.2%). Locoregional and contralateral recurrence were identified in 10.6% of TMX recipients, 6.5% of patients who switched regimens, and 5% of AI recipients. In all patients, 5.4% were diagnosed with distant metastasis, with slightly higher rates in the TMX recipients (6.4%). Multiple sites in the bone, lung, liver and brain (34.3%) was the most prevalent location of distant metastasis (DM), followed by soft tissue (20%), liver (16.2%), bone (10.5%), lung (8.6%), and other locations. Significant differences in recurrence-free survival (RFS) were observed between hormone therapy groups (p=0.004, log-rank test). Mean overall RFS was 20.4 years (95% C.I. 20.1-20.9 years). TMX recipients had a mean RFS of 19.8 years, AI recipients had a mean RFS of 18.3 years and those who switched regimens had a mean RFS of 21.9 years. Further analysis showed premenopausal patients who switched regimens had higher RFS (p=0.014). No significant difference in RFS was seen between premenopausal patients receiving AI or Tamoxifen, or amongst post-menopausal patients with different hormone therapy regimens. No significant difference in distant metastasis-free survival (DMFS) was observed between hormone therapy groups (p=0.442). Mean overall DMFS was 21.5 years (95% C.I. 21.2 - 21.8 years), with TMX patients 21.1 years, AI patients at 18.6 years, and those who switched regimens at 21.4 years. Sub-analyses of DMFS in pre and postmenopausal patients with different hormone therapy regimens showed no significant differences. Multivariate analysis showed tumor size ≤ 2cm (p= 0.0001) and negative axillary node involvement (p= 0.0001) significantly decreased odds of developing late all-type recurrence (ATR) in TMX recipients. In patients who switched regimens, Her2 positivity (p=0.04) significantly decreased the odds of late ATR. In AI recipients, not undergoing axillary operation (p = 0.008) significantly increased the odds of late ATR. For TMX recipients, negative axillary node involvement (p=0.004), tumor size ≤ 2cm (p=0.03), and undergoing mastectomy (p=0.02) significantly decreased odds of distant metastasis (DM). Among patients who switched regimens, adjuvant anti-Her2 therapy (p=0.02) significantly decreased odds of DM. For AI recipients, high PR score (p=0.02) and undergoing sentinel lymph node biopsy significantly decreased odds of DM, while age 50 years significantly increased odds of developing DM. These findings emphasize the significance of the relationship between hormone therapy regimens and factors affecting late recurrence, thereby providing valuable insights for clinical decision-making. Risk stratification based on identified factors can help in identifying patients at higher risk of late recurrence allowing for more intensive surveillance and potentially early intervention. Univariate (Chi-square, Logistic Regression) and Multivariate Analysis (Logistic Regression) for Clinicopathologic factors associated with all-type recurrence and distant metastasis after surgery and completion of 5-years endocrine therapy Table. a. LN lymph node b. SLNB, Sentinel lymph node biopsy c. ALND, Axillary lymph node dissection d. Cutoff values of Ki67 14% in KUAH and 10%in SNUH e. ER and PR cutoff value is 10% f. UV, Univariate analysis, MV multivariate analysis, O.R. Odds Ratio, C.I. Confidence Interval Citation Format: Mary Rose Mendoza, Eun-Shin Lee. Factors Influencing Late Recurrence in Breast Cancer: A Comprehensive Analysis of the Impact of Hormone Therapy Regimens abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-01-12.