In addition to their adhesive functions, cell-adhesion molecules modulate signal-transduction pathways by interacting with molecules such as receptor tyrosine kinases, components of the WNT signalling pathway and RHO-family GTPases. So, changes in the expression of cell-adhesion molecules affect not only the adhesive repertoire of a cell, but also its signal-transduction status. Conversely, signalling pathways can modulate the function of cell-adhesion molecules, altering the interactions between cells and their environment. Recent experimental evidence indicates that such processes have a crucial role in tumour progression, in particular during invasion and metastasis.