Abstract LB034: Combination immunotherapy promotes integrated anti-tumor immunity in fibrolamellar carcinoma

Abstract Fibrolamellar carcinoma (FLC) is a rare liver cancer typically arising in adolescents or young adults without underlying liver disease. Characterized molecularly by a conserved DNAJB1-PRKACA fusion oncogene and histologically by dense intratumoral stromal bands, the unique FLC tumor immune microenvironment (TIME) results in limited intrinsic anti-tumor immunity and poor clinical responses to single-agent immune checkpoint blockade. We hypothesized that the lack of robust anti-tumor immune response in FLC is mediated through two distinct mechanisms that generate both T cell exclusion and intratumoral immunosuppression. Using single-nuclear RNA sequencing from more than 110,000 cells in the FLC TIME and adjacent non-tumor liver, we found increased expression of immune checkpoint molecules and inferred cell-cell communication between CXCL12+ myofibroblasts and CXCR4+ lymphocytes. Targeting these pathways with combination CXCR4 inhibition (AMD3100) and PD-1 blockade in a human tumor slice culture model system significantly increased tumor cell death relative to isotype control and both monotherapies. Live confocal microscopy and multiplex immunohistochemistry demonstrated increased T cell activation and migration towards tumor cells with combination therapy. Single-cell RNA sequencing of treated tumor slices and spatial multi-omics further revealed an integrated immune response following combination immunotherapy involving cytotoxic T cells, helper T cells, and dendritic cells. Together, our findings demonstrate that combination CXCR4 and PD-1 inhibition cooperatively overcome both immune exclusion and immunosuppression in the FLC TIME. Furthermore, these results provide pre-clinical evidence for rational selection of combination immunotherapy in a rare tumor type that currently has no effective systemic therapies. Citation Format: Jason A. Carter, Lindsay K. Dickerson, Sara K. Daniel, Xiuyun Jiang, Heidi Kenerson, Raymond S. Yeung, Ian N. Crispe, Venu G. Pillarisetty. Combination immunotherapy promotes integrated anti-tumor immunity in fibrolamellar carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB034.