High Expression of FAP in Colorectal Cancer Is Associated With Angiogenesis and Immunoregulation Processes

Fibroblast activation protein alpha (FAP) plays an important role in tissue remodeling and helps tumor cells invade surrounding tissue. We sought to investigate FAP as a prognostic molecular marker in colorectal cancer (CRC) using immunohistochemical and transcriptomic data.FAPexpression and clinicopathological information were obtained from The Cancer Genome Atlas data set. The association ofFAPexpression and tissue cellular heterogeneity landscape was explored using the xCell method. We evaluated FAP protein expression in a cohort of 92 CRCs and 19 non-tumoral tissues. We observed thatFAPwas upregulated in tumors both at the mRNA and protein levels, and its expression was associated with advanced stages, poor survival, and consensus molecular subtype 4.FAPexpression was also associated with angiogenesis and collagen degradation. We observed an enrichment in immune-cell process-related genes associated withFAPoverexpression. Colorectal cancers with highFAPexpression display an inflamed phenotype enriched for macrophages and monocytes. Those tumors showed enrichment for regulatory T cell populations and depletion of T(H)1 and natural killer T cells, pointing to an immunosuppressive environment. Colorectal cancers with high levels of stromal FAP are associated with aggressive disease progression and survival. Our results suggest that FAP plays additional roles in tumor progression such as modulation of angiogenesis and immunoregulation in the tumor microenvironment.