PGP and neoplasm: Thus, we can suggest that MDR1 over-expression in both resistant (CB/TX or CB or 5FU) as well as in few sensitive OC tumor samples are not due to the specific chemotherapeutic drug response, rather the increased mRNA expression level is due to several stress response pathways thought to play a role in the regulation of P-gp expression (Kantharidis et al., 2000; Stordal et al., 2012).