Tumorigenesis can be recognized as altered integration of malignant cells into the host parenchyma. Tumor cell-extracellular matrix (ECM) interactions are mediated by surface receptors; integrins, nonintegrins, and proteoglycans. Integrins are a family of a-and Β-subunit glycoprotein heterodimers serving as receptors for various matrix proteins. Structurally identical integrins can bind to different ECM ligands depending on the cell type and on the state of the cell. During activation of integrins a cytoplasmic protein can be detected which undergoes tyrosine-phosphorylation. Tumor cell-endothelial cell interactions are considered as rate-limiting steps of the intra-as well as the extravasation of tumor cells during hematogenous dissemination. Tumor cell motility is one of the phases of tumor cell-matrix interaction having key importance in the metastatic cascade, including local invasion, intra- and extravasation. The data obtained from human tumors clearly indicate the importance for cytoadhesin expression in tumor progression.
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