Instead, we uncovered a novel in vivo mechanism whereby Hb-egf → Egfr signaling contributes to tumor angiogenesis: Egfr is directly activated inside tumor-associated pericytes, a mesenchymal cell type physically associated with microvascular endothelial cells, which supports endothelial cell function and integrity.49 We observe that Hb-egf secreted by cell types of the tumor stroma, either the pericytes themselves or the tumor endothelial cells, contributes to the pericyte coverage of the tumor endothelium. This evidence concerns the gene EGFR and neoplasm.