CTSB and neoplasm: As a product of glycolysis, the lactate released by tumor cells in the extracellular space is essential for the metastatic process allowing acidification of the tumor microenvironment, which is favorable for the activation of proteases such as matrix metalloproteinases (MMPs), urokinase-type plasminogen activator, and cathepsins B, D, and L inducing the degradation of the extracellular matrix (ECM) and facilitating tumor cell metastasis62.