Simultaneously, along with paracrine signals, the Ptch1 receptor in tumor stromal cells binds to the Hh ligand and activates the Hh pathway, which further transmits growth signals (VEGF, IGF, Wnt, and PDGF) to tumor cells in a feedback loop, promoting the proliferation and differentiation of tumor cells (Figure 6).189. Here, IGF1 is linked to neoplasm.