Tumor microvessels in melanoma express the beta-2 chain of laminin. Implications for melanoma metastasis

The ultrastructural localization of an amorphous matrix to the interface be tween microvessel endothelium and tumor cells has been recently reported in a series of melanomas. Laminin expression as documented by immunohistochem istry was localized to microvessels in melanomas showing the amorphous matr ix. In order to identify more precisely the type of laminin present in this amorphous material, immunostaining was carried out on cryostat sections fr om 16 human melanoma specimens. Four murine monoclonal antibodies directed against the alpha-3, beta-2, beta-3 and gamma-2 laminin chains were employe d. In the melanomas studied, alpha 3, beta 3 and gamma 2 laminin chains sho wed only minimal focal vascular positivity. In contrast, the beta 2 (16/ 16 cases) laminin chain exhibited a consistent positivity in an angiocentric pattern about tumor microvessels. In all melanomas, some tumor cells seemed to spread along the abluminal surface of the small vessels, exhibiting a p ericytic location, particularly along the intra-tumoral projections formed by the beta 2 laminin chain. Given the role of laminin in migration and tum or progression, the results suggest: a role of the beta 2 laminin chain in melanoma spread, promoting tumor migration along the abluminal surface of v essel, a phenomenon which has been termed extra-vascular migratory metastas is.