CXCR4 overexpression: An indicator of poor survival and predictor of response to immunotherapy in patients with metastatic colorectal cancer.

3546 Background: CXC-chemokine receptor 4 (CXCR4) is a ubiquitous chemokine receptor activated by the CXCL12 ligand and is implicated in tumor invasion, metastasis, and immune cell (IC) trafficking. High CXCR4 expression is associated with poor prognosis in colorectal cancer (CRC). < 10% of metastatic CRC cases harbor microsatellite instability (MSI-H) and demonstrate lower tumor mutation burden (TMB), decreased IC infiltration, and lack of response to current immunotherapy regimens. This study aims to interrogate the role of CXCR4 mRNA expression on the the tumor microenvironment (TME) and its prognostic and predictive value to tailor immunotherapeutic treatment strategies in CRC. Methods: A total of 15,026 CRC samples were analyzed using whole-exome sequencing, whole-transcriptome sequencing, and immunohistochemistry (Caris Life Sciences, Phoenix, AZ). Study cohort was stratified by CXCR4 mRNA expression levels in quartiles (Q1 (low) vs Q4 (high)). IC fraction was calculated by QuantiSeq, and real-world overall survival information was obtained from insurance claims data and calculated from tissue collection time to last day of contact. Statistical significance was determined using chi-square/Fisher-Exact and adjusted for multiple comparisons (q < 0.05). Results: Samples obtained from metastatic sites showed higher CXCR4 mRNA expression than those from primary tumors (22.7 vs 18.6 median transcripts per million (TPM), p < 0.001). CXCR4 mRNA expression was significantly lower in liver metastases than in non-liver metastases (21.2 vs 24.8 TPM, p < 0.001). Median CXCR4 mRNA expression was highest in the consensus molecular subtypes 4 (33.3 TPM) and lowest in 3 (13.0 TPM, p < 0.05). CXCR4 mRNA expression was positively associated with TMB-H, MSI-H/dMMR, and positive PD-L1 IHC status. In the TME, high CXCR4 mRNA expression was observed in tumors with a higher IC infiltration including B cells, M1/M2 macrophages, NK cells, CD8 + T cells and T-regs, regardless of MSI status. High CXCR4 mRNA expression in the primary tumor was associated with poor prognosis (HR 0.77, 95% CI 0.70-0.85; p < 0.001), regardless of MSI-status. In metastatic tumors, low mRNA expression was correlated with improved survival (HR 0.89, 95% CI 0.80-0.99; p = 0.34); however, this did not reach statistical significance in the MSS cohort (HR 0.90, 95% CI 0.80-1.0; p = 0.06). Of note, high CXCR4 mRNA expression was associated with improved survival in all patients with CRC who received pembrolizumab (HR 2.12, 95% CI 1.16-3.91; p = 0.013). Conclusions: This is the largest clinical dataset to date demonstrating high CXCR4 expression as a predictor for poor survival in CRC. Furthermore, high CXCR4 expression was associated with improved outcome after checkpoint inhibition immunotherapy, indicating its strong potential as a predictive biomarker that could inform immunotherapeutic strategies in CRC.