PCSK6 and neoplasm: Considering that PACE4 can process and activate growth stimuli and adhesion molecules in the extracellular matrix (ECM) in the manner of a secretory protein [14], the results showing that the inactivation of PCSK6 made tumor cells less competent to establish metastatic niches in the liver and finally retarded tumor growth in vivo, might in part be attributed to the presence of fewer extravasating cells from the blood wall, fewer anchored cells in liver tissue, or less active growth stimuli surrounding tumor niches.