Cancer-associated fibroblasts shape the formation of budding cancer cells at the invasive front of human colorectal cancer.

The formation of budding cancer cells at the invasive front of solid tumors is one of the first steps of metastasis. However, this process is still incompletely elucidated. Here, we used spatial molecular imaging to disentangle the complex interactions between cancer cells and the tumor microenvironment at the invasive front of colorectal tumors. Employing a 1000-plex gene panel, we defined all major cell types in tumors and adjacent normal tissue with accurate spatial information. Individual cancer cell clusters were located together, consistent with an expected mutation- and epigenetic-driven clonal evolution. However, cancer cell clusters encompassing budding cells exhibited a markedly different spatial distribution as they also contained cells that were scattered around the periphery of the main cancer cell masses. Moreover, these cells were frequently in contact with cancer-associated fibroblasts (CAFs) and underwent broad gene expression changes, mainly related to epithelial-mesenchymal transition (EMT), remodeling of the extracellular matrix (ECM), and migration. In addition, we defined an 11-gene signature (TYK2, IL2RG, KRT17, HLA-B, NPPC, WIF1, IL32, B2M, CCND1, CRIP1, ITGB1), which characterizes cancer cells en route to metastasis and is associated with inferior outcomes. Collectively, our findings suggest that CAFs induce pro-invasive gene expression changes involved in EMT, ECM remodeling, and migration.