Regulation of tumor growth as a ‘total mass' in mice: Apoptosis as a major mechanism in altering growth rates of single and multiple coexisting tumor nodules

Earlier studies have suggested that a did tumor behaves, In Its general pattern of growth, like a normal Integrated organ. In this study, the growth patterns of spherically shaped tumor nodules are re‐examlned using an accurate tumor volumemeasuring procedure, with the aim of lnveetlgattng the possible role of apoptosis in regulating tumor growth. Observations revealed at least three distinct phases at growth: rapid growth phase I, slower growth phase II and ‘stationary’ phase III. Transkion from one phase to the next was primarily due to an increase in the level of apoptosis and not to a decrease in the cell proliferation rate. The level of apoptosis, at a given phase, was similar in a single nodule and each of the multiple coexisting nodules of the same tumor line. However, temporal shifts in apoptosis levds caused early phase transition in coexisting nodules, such that their total volume was the same as that of a single nodule. it can be concluded that apoptasls appears to be a primary mechanism regulating tumor growth as a ‘total mass’, irrespective of whether the tumor exists in one or multiple nodules, if derived from the same tumor line.