Molecular aspects of the loss of cell adhesion and gain of invasiveness in carcinomas.

It has been realized that the loss of epithelial differentiation in carcinomas, which is accompanied by higher mobility and invasiveness of the tumor cells, is often a consequence of reduced intercellular adhesion. A variety of recent reports have indicated that the primary cause for the 'scattering' of the cells in invasive carcinomas is a disturbance of the integrity of intercellular junctions. It has also been suggested that during invasion, carcinoma cells convert to a sort of mesenchymal stage, as do normal epithelial cells during development. This paper discusses permanent and transient molecular mechanisms which lead to the impairment of junction integrity of epithelial cells and thus to the progression of carcinomas towards a more invasive state.