Abstract 6266: Spatial profiling of prognostic differences in the tumor microenvironment between primary and metastatic ovarian cancer using multiplexed protein imaging

Abstract Background: The tumor microenvironment (TME) plays a pivotal role in ovarian cancer (OC) progression and prognosis, while also contributing to biological differences between primary and metastatic tumors. This study examines OC TMEs to uncover associations with clinical prognosis and tumor biology by analyzing paired primary and metastatic tumors from the same patients. Methods: This study focused on 57 stage-IIIC/IV OC patients treated at the Mayo Clinic, all of whom underwent surgical debulking and adjuvant therapies. All patients provided informed consent, and the study received IRB approval. A tissue microarray (TMA) was specifically designed and constructed, containing paired primary and metastatic tissue cores from the same patients. 147 tissue cores from the constructed TMA were profiled using a 35-antibody panel, with 17 antibodies for cell phenotyping and 18 for functional state characterization. Profiling was performed using Cell DIVE, a multiplexed imaging solution at the single-cell level developed by Leica Microsystems. After cell segmentations and classifications, detailed spatial niche and regional analyses were performed at the single-cell level. Immune cell populations, as well as their TME distributions, were characterized to conduct prognostic associations and contrast primary and metastasis differences. Results: A total of 1,292,988 total cells (after excluding low-density signals and ambiguous classifications) were analyzed, with a median of 8,033 cells per core. Using spatial neighborhood analysis, 12 distinct spatial niches were identified with specific cell types and/or unique functional states. Among these, a macrophage- and fibroblast-enriched niche at the tumor-stroma interface was associated with improved overall survival (p=0.008). Another rare Treg-enriched niche, along with other immune cells, demonstrated protective effects, particularly in patients with residual macroscopic tumors after debulking surgery (p=0.05), while no significant effects were observed in those without visible residual disease (p=0.8). When comparing primary and metastatic tumors, metastatic lesions exhibited significantly increased tumor mass (p=2e-4) and a notable reduction in helper T cells (p=0.04) in tumor areas, as well as significantly increased fibroblast cells in tumor-stroma interfacing regions (p=0.002), reflecting distinct immunosuppressive and tumor-promoting shifts. Conclusion: This study reveals spatial and cellular differences in primary and metastatic OC TMEs, distribution differences linked to prognosis and surgical outcomes. These findings emphasize the potential of spatially resolved TME profiling to refine adjuvant and neoadjuvant therapeutic strategies. Citation Format: {Authors}. {Abstract title} [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 6266.