A technique to analyse the emerging zonality of heterogeneous solid tumours.

Abstract

A technique to analyse the time-dependent emergence of homogeneous regions composed of cells from a single clone within an artificial (clonally) heterogeneous tumour is described. Neoplasms were grown in vivo as xenografts made from varying proportions of the dichotomous subpopulations (Clones A and D). They were sampled frequently for volume and composition. A variable number of tumour cross-sections were taken as part of the sampling technique. The random subsamples obtained from each cross-section were enzymatically disaggregated into single cells. From the single cell disaggregates the composition of the tumours was estimated. An estimator for the global proportion of cells was then calculated from all the single cell disaggregates. Time-dependent changes in the overall composition of the tumour requires that a time-dependent estimate of the global proportions of the subpopulations be calculated from each sample. Analysis of the sample proportions results in a statistic which can be tested for goodness-of-fit against a standardized normal variate as a test of emerging zonality. Data from three artificial admixtures were examined. The results show that 'zonality', i.e. regions composed primarily of single subpopulations, emerges in all cases. However, the rate at which the zones emerge appears to depend on the 'compositional stability'. Robustness studies show that the technique is robust with respect to the global estimator of the proportion.