PGP and colorectal carcinoma: When Topo-II expression is high, Topo-II inhibitors are applicable in tumor chemotherapy and will subsequently enhance the curative effect but in the case of reduced Topo II expression, such inhibitors become ineffective because the tumor is insensitive to them.[29] Consequently, we may assume that the expression of Topo II and P-gp in CRC was related to the depth of tumor invasion in CRC patients.