Biomarker analysis from a phase I/I1b study of regorafenib and nivolumab (rego/nivo) in microsatellite stable (MSS) colorectal cancer (CRC).

188 Background: Our previous phase I/Ib study revealed modest clinical efficacy of rego/nivo in refractory MSS-CRC, implying benefits in selected populations. This has prompted us to investigate predictive biomarkers. Methods: Pre-treatment tumor samples from the previous phase Ib rego/nivo study were obtained and assessed for mRNA sequencing (RNAseq). Response-associated transcripts were identified using DESeq2 method and annotated using gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis. Results: A total of 19 pretreatment tumor samples were analyzed including 14 patients (pts) with disease control (DC) (2 partial response and 12 stable disease) and 5 pts with progression disease (PD). We observed significant upregulation of 89 genes including SFTPB ( P<0.001), SFTPA1 ( P<0.001), ERICH6B ( P<0.001) , XIST ( P<0.001), IGHV2-26 ( P<0.001), RETNLB ( P=0.005), VWA5B1 ( P=0.033), IGHV3-53 ( P<0.001), POTEH ( P=0.015), IGHV1-3 ( P=0.001) and downregulation of 70 genes including AFAP1-AS1 ( P=0.022), PRSS21( P<0.001), NTSR1 ( P<0.001), CALB1 ( P=0.033), FAM83A ( P=0.013), TBL1Y ( P=0.045), WNT7A ( P=0.022), PADI1 ( P<0.001), KRT6A ( P=0.030), KRT17 ( P=0.002) on RNA sequencing in the DC compared to PD. GO pathway enrichment analyses revealed 44 significantly upregulated pathways including positive regulation of B cell activation ( P<0.001), B cell receptor signaling pathway ( P<0.001), Phagocytosis engulfment ( P<0.001), Fc-gamma receptor signaling pathway involved in phagocytosis ( P<0.001), endocytosis ( P<0.001), immunoglobulin receptor binding ( P<0.001), serine-type endopeptidase activity ( P<0.001) in the DC compared with PD group. Nine downregulated pathways including cell-substrate junction assembly ( P<0.001), extracellular matrix (ECM) organization ( P=0.030), and ephrin receptor activity ( P=0.046) were observed in the DC compared with PD. KEGG pathway enrichment analysis revealed 8 significantly downregulated pathways including PI3K-Akt signaling ( P=0.009), ECM-receptor interaction ( P=0.006), Focal adhesion ( P=0.028), and Glycine, serine and threonine metabolism ( P=0.007) pathways in the DC compared with PD. Conclusions: RNAseq and following gene set enrichment analysis between pts with DC and PD revealed several dysregulated pathways involving immune regulation including macrophage and B cell activation, and also PI3-Akt signaling, ECM organization/receptor interaction, and adhesion, which are consistent with previous translational studies in other solid tumors. These dysregulated genes and pathways related to differentially expressed genes may need to be further evaluated as potential predictive biomarkers for rego/nivo or other tyrosine kinase inhibitor plus PD-1 blockade in MSS-CRC.