Abstract PO1-14-11: Different molecular processes are associated with recurrence in the clinical high- genomic low risk (cH/gL) and clinical low- genomic high risk (cL/gH) groups of the MINDACT clinical trial

Abstract Background: Despite the growing understanding of estrogen receptor positive/HER2-negative (ER+/HER2-) breast cancer (BC) biology, many unknowns remain regarding the mechanisms of disease recurrence. While several multigene prognostic signatures have shown clinical utility in identifying those patients at high or low genomic risk of recurrence, they can present with some limitations. In this retrospective analysis of the MINDACT trial, we interrogated the available transcriptomic data to understand which biological characteristics of the tumor are associated with recurrence in patients from the clinical high- genomic low risk (cH/gL) and clinical low- genomic high risk (cL/gH) groups (where the clinical and genomic risk were defined by a modified version of Adjuvant Online! and the 70-gene signature, respectively). Methods: These analyses focused on the subset of patients with ER+/HER2- tumors of no special type (NST) who received endocrine therapy (which comprised the majority of this NST ER+/HER2- sub-cohort) and for which central pathology and gene expression data were available (n= 1245). Scores of gene expression modules associated with key biological processes in breast cancer defined in a collection of previous publications were computed from the gene expression matrix using the formula described in Desmedt et al. (Clin. Cancer Res. 2008). Gene Set Variation Analysis method (R package ‘GSVA’ – version 1.40.1) was used to derive the enrichment scores of fifty hallmark gene sets available in the ‘H’ collection of the MSigDB database (version 7.5.1). Survival analyses were performed for disease-free survival (DFS) and distant recurrence-free survival (DRFS). Univariable and multivariable regression models, implemented by Cox regression and Fine-Gray subdistribution hazard regression methods, were performed to evaluate the association of enrichment of hallmarks and gene modules with DFS and DRFS, respectively (covariates =age, nodal status, KI67, tumor size, chemotherapy, radiotherapy). Results: DFS event occurred in 150/913 (16.4%) and 51/332 (15.4%) NST ER+/HER2- patients in the cH/gL and cL/gH groups, respectively. DRFS event occurred in 70/913 (7.7%) and 21/332 (6.3%) NST ER+/HER2- patients in the cH/gL and cL/gH groups, respectively. In the cH/gL group, we observed an association of hallmarks related to cell cycle and downregulation of gene modules related to lymphocyte-centric immune activities with worse prognosis (Table). For the cL/gH, we did not observe an association between hallmarks related to cell cycle and worse prognosis but an enrichment of hallmarks related to PI3K/AKT/mTOR signaling as well as several metabolic hallmarks related to insulin activities (Table). Of interest, in this group of patients, higher scores of the HER2-associated gene expression signature were also associated with worse prognosis. Across the two groups effects were more pronounced for DRFS than DFS. Conclusion: Different molecular processes are associated with progression in these two distinct groups of patients. The association of hallmarks related to cell cycle with survival in the cH/gL group supports the observation that adjuvant chemotherapy could benefit a subset of these patients. In the cL/gH group, the association of signatures associated with PI3K pathway and HER2 can have potential clinical relevance given their current targetability in the metastatic setting. This retrospective study is funded by the Breast Cancer Research Foundation. Table. Representative hallmarks and gene expression modules independently associated with prognosis in NST ER+/HER2- patients in the cH/gL group and in the cL/gH group #p-values reported were not corrected for multiple testing Citation Format: Christine Desmedt, Ha-Linh Nguyen, François Richard, Marion Maetens, Coralie Poncet, Laura De Meulemeester, Kim Aalders, Mauro Delorenzi, Suzette Delaloge, Jean-Yves Pierga, Etienne Brain, Suzan Vrijaldenhoven, Peter A Neijenhuis, Emiel Rutgers, Florentine Hilbers, Laura Van ’t Veer, Giuseppe Viale, Christos Sotiriou, Martine Piccart, Fatima Cardoso. Different molecular processes are associated with recurrence in the clinical high- genomic low risk (cH/gL) and clinical low- genomic high risk (cL/gH) groups of the MINDACT clinical 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 PO1-14-11.