A number of studies have demonstrated an elevation of serum or plasma protease levels in patients suffering from CRC [51-55], however, to our knowledge, the tumor marker utility of CATB, CATL, uPA and PAI-1 has not been evaluated in the same experimental setting, and compared with that of the most commonly used gastrointestinal tumor markers, such as CEA and CA-19-9. The gene discussed is CTSL; the disease is digestive system neoplasm.