Population ecology issues in tumor growth.

Mathematical models developed from population ecology are applied to tumor-host interactions and demonstrate the importance of increased efficiency in substrate absorption as a mechanism enabling tumor cells to (a) proliferate despite inefficient energy production and (b) compete successfully for resources with the numerically superior host cells. As with many biological invasions observed in nature, success of the invaders can be enhanced by disruption of the local ecology if the disruption results in decreased viability of the native populations reducing their ability to inhibit tumor cell growth either directly through an immunological response or indirectly by competition with the tumor cells for available resources. Following successful invasion and displacement of normal cells from a volume of tissue, tumor cells achieve new equilibrium states with the environment based on their efficiency of consumption and the vascularity of the tissue. Tumor therapy may be enhanced by reducing available resources below a level which will support growth of the tumor cells or above a threshold which will allow repopulation by normal cells.