Mechanisms of the invasion of normal and malignant cells

: Different examples of invasion in normal ontogenesis and during the growth of malignant genetically altered cells are discussed. The invasive migration of single epithelial cells or cell groups may be regarded as pathological variants depending on complete or partial epithelio-mesenchymal transformation. A very special new type of epithelial cell dissemination from the monolayer was observed in our experiments with epithelial cells hyperexpressing transfected RhoA gene. In these experiments, mitotic cells were squeezed out of the contracted monolayer into a fluid medium, floated passively in this medium, and settled at the substrate forming new islands. It is important to find whether this type of dissemination not associated with active cell movements can take place in tumors in vivo.