Abstract 5278: Spatial and temporal analysis of the metastatic breast cancer tumor microenvironment: from primary tumors to liver metastasis

Abstract Metastasis is a leading cause of mortality in breast cancer, with the liver being a common site for secondary tumor formation. Previous studies have demonstrated the potential to predict breast cancer liver metastases (BCLM) by identifying tumor microenvironment (TME) characteristics, including immune markers (e.g. CD8, PD1, CD206) and stromal components (e.g. αSMA, MMP8). However, the dynamic changes in the TME during metastatic progression remain elusive due to the limitations of the current tumor models. Here, we propose a longitudinal approach to monitor the temporal evolution of TME in both primary and BCLM. Using two tumor engraftment techniques, orthotopic injection of mouse breast cancer cells in a mouse mammary fat pad for primary tumor development, and portal vein injection, we modeled metastatic seeding and colonization in the liver. Live imaging (bioluminescence) of tumor progression captured the temporal dynamics of metastatic growth for early and late-stage BCLM. Tissue analysis of the primary tumor and metastatic lesions was performed using multiplex fluorescent imaging (MACsima, Miltenyi) to spatially map cellular and molecular players (e.g. immune and stromal compartments). Flow cytometry was used to quantify changes in immune cell populations. Collectively, we identified microenvironmental shifts that facilitate metastatic seeding, adaptation, and outgrowth by comparing the TME of primary tumors and liver metastases at early and late stages. Our results showed therapeutic targets within the TME, thereby offering potential strategies to disrupt the immune suppression that allows metastatic progression of breast cancer. By identifying temporal-specific alterations and key cellular players, these findings open opportunities for personalized therapies to address the evolving progression of metastatic breast cancer. Citation Format: Diana Gaete-Alvarez, Joseph Nolff, Deborah Altomare. Spatial and temporal analysis of the metastatic breast cancer tumor microenvironment: from primary tumors to liver metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5278.