Angio-tumoral complex in human malignant melanoma characterised by free laminin: ultrastructural and immunohistochemical observations.

Neo-vessel density in primary tumours as a prognostic factor for metastasis has been questioned. For this reason we have investigated qualitative aspects of tumour vascularity and particularly the association of cancer cells with endothelium, focussing on the peri-endothelial matrix. We have examined the matrix between endothelium and tumour cells in human invasive and metastatic malignant melanoma using transmission electron microscopy and immunohistochemistry. We have identified a hitherto unrecognised image (the angio-tumoral complex) in which the tumour cell and endothelium are in direct contact via an amorphous matrix. This amorphous matrix lacks an organised lamina and contains predominantly laminin with noticeably less collagen type IV. In this image endothelial cells showed no signs of physiological damage, no tumoral intravasation, and tumour cells occupied a pericytic location. This typical image was absent from naevi. We regard the laminin in this amorphous matrix as "free' laminin as distinct from laminin integrated into an organised lamina. We discuss the role of this free laminin in promoting the migration of melanoma cells in contact with vessels and suggest the possibility that this angio-tumoral complex represents a marker for metastasis.