THE IMMUNOLOGIC LANDSCAPE OF HRAS MUTANT HEAD AND NECK SQUAMOUS CELL CARCINOMA

Introduction: HRAS mutations define a distinct biologic subset of head and neck squamous cell carcinoma (HNSCC). There is limited data regarding HRAS mutant (HRAS mut) tumors' sensitivity to immunotherapy. Aim: We sought to evaluate the mutational landscape and transcriptional profile and analyze the tumor microenvironment (TME) of HRAS mut tumors to provide the conceptual framework for combinatorial treatment approaches. Methods: We analyzed mutational and transcriptome data from The Cancer Genome Atlas (TCGA). In addition, genomic DNA from baseline tumor biopsies was targeted for sequencing. Our study included 10 patients with HRAS mut and 40 with HRAS wild-type (WT) HNSCC. PD-L1 expression in FFPE tumor samples was assessed using the PD-L1 IHC 22C3 pharmDx assay. We characterized subpopulations of exhausted CD8(+) T cells by measuring the expression of T-cell Factor-1 (TCF1) and PD-1 in both the center and the periphery of the tumors using multiplex immunohistochemistry, followed by analysis using a manually trained algorithm in Qupath software. Results: The analysis of TCGA HNSCC mutation and mRNA expression data demonstrated that 6% of HNSCC harbor mutant HRAS. Transcriptome analysis showed that HRAS mut HNSCCs are infiltrated by immune cells (CD8A, CD8B, CD2) and have higher expression levels of CXCL11, CXCL10, CXCL9, and CCL4 chemokines. Moreover, the percentage of HRAS mut samples increased in higher PD-L1 score groups (11% vs. 20% vs. 100% in Tumor Positive Scores (TPS) <1%, 1-49% and ≥50% respectively, p=0.006). The analysis of TME showed that HRAS mut tumors have statistically significant higher numbers of total immune cells (5123.17/mm2vs. 3527.93/mm2, p=0.002) and a higher percentage of pre-exhausted CD8 (+) PD-1(+) TCF1(+) T Cells in the periphery (384.67/mm2vs. 51.18/mm2, p=0.040) than HRAS WT tumors. Conclusion: HRAS mut HNSCCs are characterized by a significantly increased number of pre-exhausted PD-1(+) TCF1(+) T cells and PD-L1 expression, suggesting a potential sensitivity to immunotherapy.