Ultrastructural and immunohistochemical observations concerning laminin in B16 melanoma. Is an amorphous form of laminin promoting a non hematogenous migration of tumor cells?

The gravity of cancer is related to the propensity of tumor cells to migrate from a primary site to distant organs. It is generally accepted that tumor migration occurs in the vascular stream, via the endothelial basement membrane or lamina. A recent study identified in human malignant melanomas an angio-tumoral association (termed the angio-tumoral complex) characterized by an amorphous material juxtaposed between endothelial cells and tumor cells that contained laminin. The absence of any sign of intravasation and the pericytic location of tumor cells in this typical image raised the question of the role of these complexes in promoting tumorigenesis. Using the mouse B16 melanoma model, we observed an increase of angio-tumoral complexes with tumor progression, again without any evidence of intravasation. Given the role of laminin in migration and metastasis, we discuss a non hematogenous mechanism of tumor migration along the abluminal surface of endothelium.