Analysis of extracellular matrix degradation systems has led to the insight that in cancer invasion there is often crucial interplay between cancer cells and several types of surrounding non-neoplastic stromal cells. Likewise, in normal tissue remodeling processes, the synthesis of proteolytic components is often distributed between several cell types, and there are strong similarities between neoplastic and non-neoplastic processes in the same tissue. Thus, tissue remodeling events are excellent models for studies of extracellular proteolysis in cancer. This has become even clearer by recent analyses of genetically modified mice.