Invasive activities of metastasizing and nonmetastasizing tumor cell variants in vitro

Pieces of the endothelium of the aorta of BDX rats were confronted with two syngeneic-tumor-cell variants. While the AS variant is non-metastasizing, the ASML cells metastasize spontaneously via the lymphatic vessels. By means of scanning-electron microscopy the adhesion phenomena and the various stages of invasive activity of the non-metastasizing variant (AS) as well as the retraction of the endothelial cells depending on the time of confrontation were studied. Though the metastasizing variant (ASML) adhered firmly to the endothelium, we found neither signs of invasive activity of these tumor cells nor retraction phenomena of the endothelial cells. Aggregates of AS- and clusters of ASML-cells, respectively, behaved in exactly the same way as single cells: while the ASML-clusters remained inactive, the AS-aggregates exhibited invasive activities. Those cells which were in intimate contact with the endothelium started to leave the aggregate, thereby forming a foot-like layer beneath the rest of the aggregate; these cells began to invade.