Clinical relevance of clinical treatment score post 5 years (CTS5) in HR-positive, HER2-positive breast cancer: An exploratory analysis from the HERA trial.

519 Background: The clinical treatment score post-5 years (CTS5) has proven valuable in assessing the necessity for extended endocrine therapy among patients with early-stage hormone-receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer. This study aimed to explore the potential of CTS5 as a predictive tool for long-term survival beyond five years in patients with specifically HR-positive, HER2-positive breast cancer. Methods: We collected patient-level data from the HERceptin Adjuvant (HERA) (BIG1-01; NCT00045032) trial. Our investigation focused on assessing the risk of late distant recurrence (DR) and overall survival (OS) according to the CTS5 risk score as continuous value and CTS5 stratification risk groups. Furthermore, we performed a Cox-regression analysis to determine the prognostic performance of CTS5, stratifying subgroups by age and administration of trastuzumab. Results: A total of 1,818 patients with HR-positive, HER2-positive breast cancer were included in this analysis. The CTS5 score, as a continuous variable, emerged as an independent prognostic factor for both late DR (adjusted HR, 2.04; 95% CI, 1.62-2.57; P < 0.001) and OS (adjusted HR, 2.02; 95% CI, 1.58-2.58; P < 0.001), respectively. In addition, multivariable analysis showed a significant association between the high-risk group and adverse outcomes in late DR (adjusted HR, 2.76; 95% CI, 1.84-4.15; P < 0.001) and OS (adjusted HR, 2.45; 95% CI, 1.60-3.74; P < 0.001) compared to low/intermediate group. Consistent results were observed, regardless of age or administration of HER2-targeted therapy. Conclusions: CTS5 is a useful prognostic tool for predicting late DR and OS in HR-positive, HER2-positive breast cancer patients. Extension of endocrine therapy should be actively considered in patients with CTS5 high-risk group.