Invasion of human embryonic fibroblast cell aggregates by rat tumor cells of different metastatic capacities.

Aggregates of normal human Wi38 cells are used as a three dimensional substrate to test in vitro the behavior of rat tumor cells which exhibit different invasive and metastatic capabilities in vivo. The invasive but non metastatic tumor cells colonize the Wi38 cell aggregates, invade and destroy them within three days. The non invasive but highly metastatic tumor cells settle in a limited number on the aggregates but show no further activities. Co-cultivation of these tumor cells with cell suspension of single Wi38 cells under aggregation conditions does not hinder the Wi38 cells in forming aggregates. The results show that the invasive process in the metastatic cascade needs more specific reaction partners and host environment than local tumor growth. The conditions of the first process cannot be mimicked by a simple model.