growth factor role A role that stimulates a cell to grow or proliferate. Most growth factors have other actions besides the induction of cell growth or proliferation. Extracellular polypeptide signal molecule that can stimulate a cell grow or proliferate. Examples are EGF and PDGF. Most growth factors also have other actions. GO:0008083 Growth Substance IMR:0000030 (obsolete) role related to changing size