GPA33 and colorectal carcinoma: Meanwhile, immunotoxins targeting TAAs of CRC, such as CEA, EGFR (epidermal growth factor receptor), GPA33 (glycoprotein A33), mesothelin and EpCAM (epithelial cell adhesion molecule) with various toxins including PE38, PE24 or α-sarcin, have achieved promising results in the preclinical and clinical studies [22–25].