Progression to tumour malignancy involves changes in a tumour cell's capabilities to adhere and communicate with neighboring cells and with its extracellular environment. Correlation studies in human cancer specimen and functional experiments with cultured tumour cells and transgenic mouse models have indicated that the loss of the cell adhesion molecule E-cadherin is causally involved in the formation of epithelial cancers (carcinomas). More recently, it has been observed that the function of E-cadherin is replaced or overruled by the expression of mesenchymal cadherins, such as N-cadherin. Although the functional implication of such a 'cadherin switch' remains to be elucidated, recent experimental results demonstrating an interaction of cadherins with tyrosine kinase receptors suggest that changes in cadherin expression may not only modulate tumour cell adhesion but also affect signal transduction and, hence, the malignant phenotype.