On the Cover Matrix metalloprotease 9 (MMP-9)/Gelatinase B process a variety of extracellular matrix proteins and is focally upregulated in macrophages in connection with necrosis in liver metastases from colorectal adenocarcinomas. MMP-9 expressing tumor edge macrophages were present in the primary tumors but not in their liver metastases. MMP-9 mRNA was detected with radiolabeled probes using in situ hybridization. For details, see article by Illemann et al. on page 293.