CTSS and cancer: Among these proteolytic enzymes, cysteine proteases, such as cathepsins, papain, and calpains, are widely distributed in tissues and have various functions, including degradation of extracellular matrix, modulation of immune response, tissue development, and induction of monocytes and cancer cells.3, 4, 5 Cathepsins are intracellular cysteine proteases that function in protein degradation in lysosomes6 and secretory granules.