Abstract PO1-15-07: Subtyping-directed precision treatment refines traditional one-size-fits-all therapy in HR+/HER2- breast cancer: a sub-study of the MULAN umbrella trial

Abstract Background: The standard approach of using one-size-fits-all endocrine therapy for hormone receptor-positive and HER2-negative (HR+/HER2-) breast cancers has faced significant challenges due to variations in treatment response among individuals. Consequently, there is still an urgent need to understand the molecular biology of HR+/HER2- breast cancer and explore precision treatment strategy. Methods: We established a multiomics cohort (n = 351), multicenter real-world clinical cohorts (n = 643), a prospective clinical cohort (MULAN trial), and a drug-testing platform containing patient-derived organoids (n = 126) and patient-derived tumor fragments (n = 49) of HR+/HER2- breast cancers. Integrating "bench" and “bedside” data, we conducted comprehensive preclinical and clinical translational research on precision strategies in HR+/HER2- breast cancer. Results: We implemented a comprehensive classification system for HR+/HER2- breast cancer, comprising four distinct subtypes. We further demonstrated the efficacy and mechanisms of subtyping-directed precision treatment strategies through clinical cohort studies, omics analysis and functional assays: endocrine therapy alone for the canonical luminal subtype; the addition of CDK4/6 inhibitor and PARP inhibitor for the proliferative subtype; the immunotherapy for the immunogenic subtype; and tyrosine kinase inhibitors for the receptor tyrosine kinase-driven subtype. Using clinically applicable subtyping methods, we validated that matched precision treatment strategies outperformed unmatched approaches in a real-world cohort, almost doubling the median progression-free survival time for patients with refractory advanced HR+/HER2- breast cancer (9.83 months [95% CI, 5.74-13.93] vs 4.77 months [95% CI, 3.35-6.18]; hazard ratio 0.64 [95% CI, 0.41-0.99]). Importantly, the first-stage analysis of the MULAN phase II umbrella clinical trial (NCT04355858) verified the higher objective response rate (88.9%, 95%CI: 51.7%-99.7%) of the subtyping-directed precision treatment. Conclusion: Our study emphasizes the superiority of subtyping-directed precision treatment strategies for HR+/HER2- breast cancer, refines traditional “one-size-fits-all” therapy, and facilitates the translation of precision treatment strategies from bench to bedside. Overall study design Part 1 Subtype Molecular Characteristics: Molecular features of the four subtypes of HR+/HER2- breast cancer. Part 2 Multidimensional Efficacy Validation: Integrating data from a multiomics cohort, real-world study, drug testing platform and prospective clinical research to validate the subtyping-directed precision treatment strategy in HR+/HER2- breast cancer. Part 3 Subtyping-directed Precision Treatment Strategy: Integrating clinical cohort studies, omics analysis and functional assays revealed the heterogeneity of treatment response in HR+/HER2- breast cancer, and proposed a subtyping-directed precision treatment strategy. CIN, chromosomal instability; RTK, receptor tyrosine kinase; CNA, copy-number alteration; ER, estrogen receptor; HR, hormone receptor; HER2, human epidermal growth factor receptor 2. Citation Format: Xiu-Zhi Zhu, Xi Jin, Hu-Yun-Long Zhang, Xiyu Liu, Yi-Fan Zhou, Yi-Yu Chen, Tong Fu, Ming-Liang Jin, Ya-Xin Zhao, Yi-Fan Xie, Ruo-Xi Wang, Zhong-Hua Wang, Lei Fan, Yi-Zhou Jiang, Zhi-Ming Shao. Subtyping-directed precision treatment refines traditional one-size-fits-all therapy in HR+/HER2- breast cancer: a sub-study of the MULAN umbrella trial [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 PO1-15-07.