ABSTRACT

Tissue sizing is a process of negative feedback inhibition in which the growth rate of a cell behaves as if it were controlled by the momentary size or population density of the multicellular community to which the cell belongs. Sizing was first identified by Ellis (1909) in studies of vertebrate regeneration.1 It has since been documented in a wide variety of embryonic, postnatal, regenerative, and compensatory growth processes at the organismic, organ, and tissue levels in a broad spectrum of metazoans ranging from cnidarians to mammals. Tissue sizing is the single most common mechanism of growth regulation that has been identified in normal tissues. Its role in neoplastic growth regulation is unknown. Sizers can be identified experimentally by transplanting innocula of varying sizes into host animals and determining whether their subsequent growth is a function of momentary size alone, or whether it also depends on time or initial conditions.