Abstract PD11-05: PD11-05 Gut microbiome signatures correlate with overall survival among patients receiving eribulin with or without pembrolizumab for hormone receptor-positive metastatic breast cancer
Authors: Barroso-Sousa Romualdo , Li Tianyu , Damania Ashish V. , DiLullo Molly K. , Keenan Tanya , Wulf Gerburg M. , Spring Laura M. , Mittendorf Elizabeth A. , Ligibel Jennifer A. , Ajami Nadim J. , Wargo Jennifer , Tayob Nabihah , Tolaney Sara 
Published: March 2023

Abstract
Background: The gut microbiome modulates response and resistance to immune checkpoint inhibitors (ICI) across different cancer types. The objective of this study was to explore the association between fecal microbiome profiles and clinical outcomes in patients with hormone receptor-positive (HR+) metastatic breast cancer (MBC) treated with eribulin (E) + pembrolizumab (P) or E alone as part of a randomized phase II study (NCT03051659). Patients and Methods: Metagenomic shotgun sequencing was performed on fecal samples collected prior to randomization from a subset of 26 participating patients (E+P, n = 15; E, n = 11) collected prior to randomization. Sequencing data were processed with MetaPhlAn3 to obtain diversity scores and taxonomic composition profiles. Associations between microbiome diversity, taxonomic composition, and clinical outcomes including survival metrics were assessed using Kaplan-Meier estimation methods and Cox proportional hazard models. Results: In this subset, median follow-up was 21.6 months and median overall survival (OS) was 17.9 months. OS was not statistically significant between two treatment arms as observed in the overall cohort. Metagenomic microbiome analysis revealed higher alpha diversity by inverse Simpson Index values associated with longer survival among all patients (p = 0.004), and in patients in the E + P arm (p = 0.006) but not in the E arm (p = 0.2). At the taxonomic level, longer OS among all patients was associated with a baseline lower relative abundance of Blautia wexlerae (≤0.2%vs &gt;0.2%) (22.1 vs 16.6 months; p = 0.01) and a higher relative abundance of Odoribacter splanchnicus, a common short-chain fatty acid producing gut bacterium (&gt;0.35% vs ≤0.35%) (22.3 vs 11.3 months; p &lt; 0.0001). These associations remained significant after controlling for age, ECOG-PS status, and use or not of prior lines of chemotherapy in the metastatic setting. Conclusions: These results suggest high diversity and composition of the gut microbiome are associated with prolonged OS in HR+ MBC pts receiving eribulin with pembrolizumab. Additional and larger clinical studies are needed to validate these findings and preclinical models are needed to interrogate the mechanisms by which gut microbiome diversity and composition may impact therapeutic response and clinical outcomes in this patient population.
Citation Format: Romualdo Barroso-Sousa, Tianyu Li, Ashish V. Damania, Molly K. DiLullo, Tanya Keenan, Gerburg M. Wulf, Laura M. Spring, Elizabeth A. Mittendorf, Jennifer A. Ligibel, Nadim J. Ajami, Jennifer Wargo, Nabihah Tayob, Sara Tolaney. PD11-05 Gut microbiome signatures correlate with overall survival among patients receiving eribulin with or without pembrolizumab for hormone receptor-positive metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD11-05.