Premetastatic uveal melanoma cells do not express laminin receptors

Interactions between extracellular matrix and tumor cells are of great importance for tumor cell invasion. They are mediated by cellular surface receptors (integrins). As the glycoprotein laminin enhances invasion in some neoplasms and as the expression of laminin receptors is sometimes correlated with the invasive activity, the tumor cell-laminin receptor-laminin cascade could play a key role in melanoma cell spread as well. We therefore investigated 12 uveal melanomas with a monoclonal anti-laminin-receptor antibody. In all, 9 tumors demonstrated no reaction and 3 exhibited just a partial and slight reaction. Endothelial cells within the melanomas were laminin-receptor-positive. As laminin is found primarily in basement membranes, laminin receptors are expressed mainly by cells in contact with these structures, e.g., endothelial, epithelial, and carcinoma cells. The nonepithelial uveal melanomas, which produce only little basement membrane material, if any, seem to have no need for laminin receptors, at least provided that basement membranes do not have to be traversed. As a result, laminin receptors are not expressed.