Cytoskeletal reorganizations, especially alterations of contractile tension generated by the actin-myosin cortex, are of central importance in the development of the phenotype of morphologically transformed neoplastic cells with invasive behavior. These reorganizations can be regarded as genetically determined aberrations of the physiological reactions of normal cells which are responsible for their ability to undergo exploratory migrations, including epithelio-mesenchymal transformations, invasion of matrix by epithelial tubules etc. It is suggested that these physiological and neoplastic transformations are based on Rho-dependent alterations in contractility. A decrease or an increase in contractility may result in the development of distinct types of invasive phenotypes. These contractility-dependent phenotype alterations may be modified by alterations in the expression of other genes, especially of those coding for components of adhesive structures.