It is also known that CTSL processes pro-HPSE (inactive) into HPSE (active), once both protein complexes have been secreted into the extracellular milieu, and is super-expressed in various types of tumors, such as glioma, melanoma, and liver, breast and prostate cancer, and activates HPSE through a proteolytic mechanism. This evidence concerns the gene CTSL and central nervous system cancer.