Environmental stress induced by the tumor bed effect leads to subpopulation exclusion within heterogeneous neoplasms: modeling studies.

Three nested mathematical models were used to describe the compositional stability of subpopulations within artificial heterogeneous neoplasms in a stressed environment. The first models a microecology in which each subpopulation grows independently and no competition for resources occurs. In the second model, subpopulations compete for common resources, while in the third, the subpopulations compete for resources, and an additional dynamic term describes the emergence of the second population from the first. Environmental stress is a consequence of ionizing radiation damage to the normal tissue in which the tumor grows (the tumor bed effect, TBE). Compositional data observed as a function of time from experimental assays of artificial heterogeneous colon adenocarcinoma xenografts were used for this theoretical analysis. The results show that in the stressed environment, tumor subpopulations do compete for common resources, and that the "weight of competition" (i.e., the rate at which competition can retard total growth) is significantly enhanced. In contrast to unperturbed artificial heterogeneous tumors which exhibit stable composition as a function of time, TBE stress leads to selection of the majority neoplastic population.