Plasticity of tumor cell migration: acquisition of new properties or return to the past?

During tumor development cancer cells pass through several stages when cell morphology and migration abilities change remarkably. These stages are named epithelial-mesenchymal and mesenchymal-amoeboid transitions. The molecular mechanisms underlying cell motility are changing during these transitions. As result of transitions the cells acquire new characteristics and modes of motility. Cell migration becomes more independent from the environmental conditions, and thus cell dissemination becomes more aggressive, which leads to formation of distant metastases. In this review we discuss the characteristics of each of the transitions, cell morphology, and the specificity of cellular structures responsible for different modes of cell motility as well as molecular mechanisms regulating each transition.