The proteolytic enzymes of the extracellular matrix, lysosomal cysteine proteases such as cathepsins B and L, as well as their endogenous inhibitors, cystatins, for example, cystatin A (also known as stefin A), cystatin B, and cystatin C, may play important roles in cancer progression and metastasis [5]. The gene discussed is CTSB; the disease is cancer.