The target of cathepsin X carboxypeptidase activity in brain cells is γ-enolase, which plays an important role in aerobic glycolysis and cell proliferation [45,66,67]; γ-enolase is overexpressed in neurogenic and neuroendocrine tumors [68], and in this study and in others [49], it was shown that it is also expressed in GBM tissues. Here, CTSZ is linked to neuroendocrine neoplasm.