IL6 and neoplasm: Paracrine ligand-dependent Hh signaling requires endogenous ligands to bind stromal cell PTCH receptors thereby initiating the release of growth signals such as interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), bone morphogenetic protein (BMP), and insulin-like growth factor (IGF) to promote tumor progression (Sari et al., 2018).