Basement membranes in cancer.

Basement membranes are ubiquitous tissue constituents which occur as supportive structure adjacent to epithelium, endothelium, mesothelium and also around smooth as well as striated muscle cells, Schwann cells and fat cells. In various types of cancer, basement membranes have been extensively studied by electron microscopy. Often basement membrane interruptions were seen in invasive neoplasms but in some tumors the neoplastic cells were surrounded by a continuous basal lamina. Recent immunocytochemical studies have shown that in invasive carcinomas the neoplastic cells often lack a continuous basement membrane. This may be caused by catabolic activity of invasive tumor cells, which have been shown to produce specific collagenases, or by insufficient production and/or extracellular assembly of basement membrane components by the neoplastic epithelial cells. In diagnostic histopathology, immunocytochemical staining of basement membrane components such as type IV collagen and laminin may help to distinguish between noninvasive (benign or in situ) and invasive lesions. Furthermore, in carcinomas the extent of the expression of basement membrane components may be correlated with the degree of differentiation of the neoplastic cells. Finally, in soft tissue tumors, basement membrane staining may be helpful for the differentiation of basement membrane producing neoplasms (e.g. of vascular, neural, smooth muscle or striated muscle origin) from non-basement membrane producing neoplasms (e.g. of fibroblastic origin).