title: Many growth factors may not be growth factors.
abstract: Both organ growth and tumor growth are dependent upon a biased ratio of cell births to cell deaths; this ratio is independent of the frequency of mitosis. Thus, so-called growth factors that affect only the frequency of mitosis are not really growth factors. I shall advance two hypotheses: that the normal adult ratio of cell births to cell deaths is maintained by the activity of a factor or factors produced by the stem cells; and that the differentiating cells, as well as the stem cells, produce a different factor that limits the frequency of mitosis.
authors.affiliation: Department of Pathology, University of Washington, Seattle 98195.
authors.forename: R T
authors.initials: RT
authors.lastname: Prehn
mesh_terms: D000818:Animals; D016923:Cell Death; D002454:Cell Differentiation; D002455:Cell Division; D006133:Growth Substances / Q000502:physiology*; D006801:Humans; D008938:Mitosis; D009369:Neoplasms / Q000473:pathology*; D011230:Precancerous Conditions / Q000473:pathology
chemical_list: D006133:Growth Substances