EGF and neoplasm: 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.