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growth factor Any of various chemicals, particularly polypeptides, that have a variety of important roles in the stimulation of new cell growth and cell maintenance. They bind to the cell surface on receptors. Specific growth factors can cause new cell proliferation (epidermal growth factor, insulin-like growth factor, haemopoietic growth factor – see haemopoietic tissue) and the migration of cells (fibroblast growth factor) and play a role in wound healing (platelet-derived growth factor; PDGF). Some growth factors act in the embryonic stage of development; for example, nerve growth factor stimulates the growth of axons and dendrites from developing sensory and sympathetic neurons. It is thought that some growth factors are involved in the abnormal regulation of growth seen in cancer when produced in excessive amounts.