[Changes in the growth characteristics of mouse and rat fibroblasts during tumor progression]

Changes in growth characteristics (the growth in a mat of normal cells, contact inhibition of division, growth-substrate dependence, dependence on the serum growth factors) and tumourigenicity were compared in 6 cells lines of mice and rats during their in vitro and in vivo long passages. All these factors progressed independently of a tumourigenicity increase, i.e. they obeyed the Fould principle. The trait responsible for the cell capacity to proliferate on a layer of normal cells proved to be the most correct one relative to tumourigenicity prediction.