THE BASEMENT-MEMBRANE AND ITS INVOLVEMENT IN CARCINOMA CELL INVASION

During the development of invasive cancer, carcinoma cells have to pen etrate the extracellular matrix including the basement membrane (BM). This is a usually continuous layer composed of a dense meshwork of col lagens, glycoproteins and proteoglycans. It normally underlies epithel ia and lacks any pores large enough to allow epithelial cells to pass through them. In consequence, the invasion of carcinoma cells through the BM must be either an active process effected by the carcinoma cell s themselves or is mediated by structural alterations of the BM occurr ing during carcinogenesis and cancer progression. It was supposed by m any authors that invading and metastasizing carcinoma cells are able t o degrade actively the continuous, uninterrupted BM by secreting type IV collagenase and other proteolytic enzymes. Although there is a weal th of experimental evidence which fits the concept that the active deg radation of the BM is an essential requirement for carcinoma cell inva sion and metastasis, certain data do not agree with this hypothesis. T hus, it is still doubtful whether active lysis of the BM by carcinoma cells is actually a prerequisite for invasion and metastasis or whethe r there are alternative and/or additional mechanisms favoring the inva sion of carcinoma cells.