Abstract 4654: Clinical significance of tumor infiltrating lymphocytes and neoadjuvant chemotherapy in colorectal cancer liver metastases

Abstract Background: The effects of neoadjuvant chemotherapy (NAC) and the survival impact of tumor infiltrating lymphocytes (TILs) in the colorectal cancer liver metastases (CRCLM) tumor microenvironment (TME) remain poorly understood. Methods: We studied the clinicopathologic characteristics and the levels of different TIL subpopulations using multiplexed quantitative immunofluorescence (mQIF) in paired primary/liver metastasis in two independent CRCLM cohorts from Yale-New Haven Hospital between 2000-2024 using tissue microarrays. The first cohort included 84 patients (Cohort 1) and the second cohort comprised 95 patients (Cohort 2). The mQIF analysis included the markers DAPI for all cells/nuclei, cytokeratin (CK) for tumor epithelial cells, CD4 for helper T-cells, CD8 for effector T-cells, and FOXP3 for regulatory T-cells (Tregs). The levels of different cell populations were measured in specific tumor tissue compartments including the CK+ cancer-cell nests, the CK-negative peritumoral stroma and the total tissue area. The association between TILs and treatment-specific overall survival (OS) were analyzed. Results: The OS was comparable between cases treated with or without NAC with a median OS after stage 4 diagnosis in NAC treated and not treated of 84 vs. 65 months, p = 0.31 and 59 vs. 115 months, p = 0.23 in Cohorts 1 and Cohort 2, respectively). NAC was associated with significantly higher CD8+ TILs in liver metastases in all studied tumor tissue compartments (p < 0.05 in Cohort 1 and p < 0.003 in Cohort 2). Elevated CD8+ TILs in the cancer-cell compartment of CRC liver metastases were associated with significantly improved survival irrespective of NAC (Hazard Ratio (HR) = 0.39, p = 0.022 in Cohort 1 and HR = 0.25, p = 0.025 in Cohort 2), a pattern not observed in primary tumors of both cohorts. In contrast, Tregs were consistently lower in liver metastases compared to primary tumors across all compartments (p < 0.0001 in both cohorts). Patients who did not have disease recurrence after NAC and hepatectomy had higher levels of CD8+ T-cells in liver lesions compared to those with tumor recurrence (p = 0.05 and 0.04 in Cohort 1 and 2 respectively). Microsatellite instability-high (MSI-H) tumors exhibited higher CD4+ and CD8+ TILs in primary tumors, but not in liver metastases (n = 5, p < 0.05 and < 0.01 for CD4+ and CD8+ T cells, respectively, across all compartments). Conclusion: NAC did not show survival benefit in CRCLM patients but was associated with increased effector TILs in liver metastases. Elevated CD8+ TILs in CRCLM are prognostic and this highlights the potential for immunostimulatory strategies to leverage TME changes induced by NAC. Liver metastatic MSI-H CRCs show prominent inter-tumor heterogeneity with increased TILs only in the primary lesion. Citation Format: Yasaman Rezaie, Kerryan Ashley, Janie Zhang, Thejal Srikumar, Jassim DiPalermo, Kurt Schalper, Michael Cecchini. Clinical significance of tumor infiltrating lymphocytes and neoadjuvant chemotherapy in colorectal cancer liver metastases [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 4654.