Ultrastructural and immunohistochemical studies of the periendothelial matrix in human melanoma: evidence for an amorphous matrix containing laminin

Angiogenesis and the extracellular matrix are fundamental to tumor progress ion from in situ to invasive and metastatic disease. Laminin, a major glyco protein integrated into basement membranes, is observed in angiogenesis and tumorigenesis. A recent study described an association between melanoma ce lls and endothelial cells via an amorphous matrix containing laminin. In th e current study, we have examined 45 cases of human primary and metastatic melanomas by electron microscopy for the presence of an amorphous matrix. W e observed an amorphous matrix without a clearly delineated lamina or basem ent membrane in 41 of the 45 melanomas studied. 28 cases with tissue blocks available for study were examinated by immunohistochemistry for the expres sion of laminin and type IV collagen. We observed the presence of an angioc entric matrix containing laminin in 24 of the 28 melanomas studied. Since l aminin is involved in tumor migration, the presence of laminin between mela noma cells and small vessels suggests a role for this material in periendot helial tumor migration. However, further study is required to characterize the nature of this material and the mechanisms involved.