Abstract: Chemotherapy is one of the most important methods of cancer treatment. However, multidrug resistance (MDR) has been the main factors affecting their efficacies. Recent studies show that the amplification of MDRl gene in tumor cells, the over expression of the related drug resistance protein and the cell cycle and apoptosis pathway in signal transduction are the main causes for the failure of chemotherapy.

Key words:  Drug resistance, neoplasms, Multidrug resistance-associated proteins, Cell cycle, Neoplastic stem cells