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 progression from in situ to invasive and metastatic disease. Laminin, a major glycoprotein integrated into basement membranes, is observed in angiogenesis and tumorigenesis. A recent study described an association between melanoma cells and endothelial cells via an amorphous matrix containing laminin. In the current study, we have examined 45 cases of human primary and metastatic melanomas by electron microscopy for the presence of an amorphous matrix. We observed an amorphous matrix without a clearly delineated lamina or basement membrane in 41 of the 45 melanomas studied. 28 cases with tissue blocks available for study were examined by immunohistochemistry for the expression of laminin and type IV collagen. We observed the presence of an angiocentric matrix containing laminin in 24 of the 28 melanomas studied. Since laminin is involved in tumor migration, the presence of laminin between melanoma cells and small vessels suggests a role for this material in periendothelial tumor migration. However, further study is required to characterize the nature of this material and the mechanisms involved.