CTSB and melanoma: Accordingly, the lower pH in the tumormicroenvironment induces the relocation of cathepsin B-containingvesicles to the cell surface and the release of their content intothe extracellular space.25,58 Additionally, the enzymeis secreted by tumor-associated benign cells such as macrophages,fibroblasts, osteoclasts, T-lymphocytes, and endothelial cells.59,60 The correlation between cathepsin B activity and the metastaticpotential in B16 melanoma cells was demonstrated 40 years ago.61