Abstract B012: Spatial immune correlates of response to eribulin and pembrolizumab in metastatic triple negative breast cancer on the ENHANCE1 trial
Authors: Vanguri Rami , Foong Yee Hoon , Wang Qi , Chen Diane , Kearney Matthew , Guo Hua , Garlin Michelle , Connelly Courtney , Tolaney Sara , Kalinsky Kevin , Connolly Eileen 
Published: February 2025

PD-L1 is the only approved biomarker for pembrolizumab in metastatic breast cancer for response to combination chemo-immunotherapy. We searched for tissue-based immune biomarkers of response in metastatic triple negative breast cancer (mTNBC) patients prospectively treated with front-line combination chemoimmunotherapy on the ENHANCE-1 study with eribulin and pembrolizumab. We used quantitative multiplexed immunofluorescence (qmIF) to evaluate immune populations in pre-treatment tissue and characterize associations to clinical outcomes. ENHANCE-1 was a single arm phase Ib/II trial which evaluated the efficacy and safety of eribulin and pembrolizumab in 167 patients with mTNBC who had received 0-2 prior lines of therapy (66 patients in the first line setting [stratum 1] and 101 patients with 1-2 prior lines of therapy [stratum 2]). 142 patient samples were evaluable for our study: 58 samples from stratum 1 and 84 samples from stratum 2. Objective response rate (ORR) was defined as percentage of patients with either complete response (CR) or partial response (PR) by RECIST 1.1. The ORR was 25.8% in stratum 1 and 22.5% in stratum 2 for the 142 patients analyzed. Fresh tissue biopsies were not required immediately prior to enrollment on ENHANCE-1. As the tumor microenvironment can be heavily modulated by intervening treatments, we only evaluate samples which were taken immediately before enrollment. We also excluded patients in which only lymph node tissue or pleural fluid was submitted. 43/142 patient samples satisfied these criteria: 31 out of 43 from stratum 1 and 12 out of 43 from stratum 2. We used qmIF to stain whole tissue sections with: CD4, CD8, FoxP3, CD56, CD20, CD163, CD68, Vimentin and HLA-DR to identify biomarkers associated with patient response evaluated with the RECIST criteria. Halo (Indica labs) was used to segment and threshold cells for positive markers as well as to identify tumor and stromal tissue areas. We define responders as those with a complete or partial response. Non-responders are defined as patients with stable or progressive disease. Our analysis revealed that increased stromal CD56+ density, a marker of NK cells, was significantly associated poor response (p=0.047). Increased density of stromal vimentin-expressing CD68+ was associated with patients who achieved response to therapy (p=0.005). Enrichment of stromal CD56+ cells compared to cells expressing either CD163+ or CD68+ cells was associated with a lack of response to therapy (p=0.014). Our study highlights the role of the tumor microenvironment, particularly the stromal immune cell composition, in influencing the response to eribulin and pembrolizumab in mTNBC patients. The identification of stromal CD56+ cells as a marker of non-response and stromal vimentin-expressing CD68+ cells as a marker of response provides valuable insights into the mechanisms of action and resistance to this therapeutic combination. These findings could potentially guide the development of more personalized treatment strategies and improve clinical outcomes for patients with mTNBC.

Citation Format: Rami Vanguri, Yee Hoon Foong, Qi Wang, Diane Chen, Matthew Kearney, Hua Guo, Michelle Garlin, Courtney Connelly, Sara Tolaney, Kevin Kalinsky, Eileen Connolly. Spatial immune correlates of response to eribulin and pembrolizumab in metastatic triple negative breast cancer on the ENHANCE1 trial [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B012.