Abstract CT141: Combination of hormone therapy, GnRH agonist, and immunotherapy enhance immune activation in premenopausal ER+/HER2- metastatic breast cancer patients: Results of biomarker analysis from a pilot phase II study

Abstract

Abstract Introduction: Immunotherapy has not been proved to be efficacious in ER+/HER2- metastatic breast cancer. Our team has reported an effective combination of exemestane, gonadotropin releasing hormone agonist, and pembrolizumab in premenopausal ER+/HER2- MBC. Here we report the updates of the final results and biomarker associates of the study. Methods: Premenopausal ER+/HER2- MBC patients who failed no more than 2 lines of hormone therapy without chemotherapy for MBC were enrolled in a tertiary medical center in Taiwan (NCT02990845). The primary endpoint was progression-free survival (PFS) rate at 8 months. The secondary endpoints included overall response rate, overall survival (OS), progression-free survival (PFS), and other biomarkers. Pre-treatment (N=12) and post-treatment (N=5) tumor tissue were collected for biomarker analysis, including tumor-infiltrating lymphocyte(TIL), PD-L1 expression by immunohistochemical staining, tumor mutational burden, RNAseq, and IO360 analysis. Results: A total of 15 patients were enrolled in the study with 14 evaluable patients. The progression-free survival rate at 8 months was 64.3%. The median PFS and OS were 10.34 months and 39.56 months respectively. The overall response was 35.7%. TIL, tumor mutational burden, or PD-L1 expression were not associated with the response to the treatment. In the NanoString IO-360 analysis, increased expression of genes in the immune related signature was noted in the post-treatment samples as compared to the pre-treatment samples. The expression levels of MHC class II and T cell-related genes were upregulated in the post-treatment samples. Most of the immune cell populations are increased after pembrolizumab/exemestane/leuprolide treatment. CD56 dim NK cells, Th1 cells, and NK cells are the top 3 populations that are increased after treatment. Using CIBERSORT algorithms to analyze RNAseq data from pretreatment samples, dendritic cells (p=0.039) and NK cells (p=0.082) were associated with the responders versus non-responders in the study. Conclusion: In this final analysis, pembrolizumab, exemestane, and leuprolide remain an effective treatment for premenopausal ER+/HER2- MBC. Pembrolizumab, exemestane, and leuprolide treatment is associated with immune system activation, turning the tumor microenvironment from cold to hot in luminal disease. Citation Format: I-Chun Chen, Ching-Hung Lin, Dwan-Ying Chang, Tom Wei-Wu Chen, Ming-Yang Wang, Wei-Li Ma, Yi-Ting Lin, Shu-Min Huang, Yen-Shen Lu. Combination of hormone therapy, GnRH agonist, and immunotherapy enhance immune activation in premenopausal ER+/HER2- metastatic breast cancer patients: Results of biomarker analysis from a pilot phase II study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT141.