It was estimated that in 2008, 1,437,180 patients would receive a new cancer diagnosis and treatment of individuals would die of cancer (Jemal et al. 2008). Since the vast majority of patients dying of cancer will have had anticancer therapy, both conventional chemotherapy and novel targeted therapy, it can be concluded that these patients are dying with drug resistant cancer. The term multidrug resistance is also apt – in that these patients die after having undergone multiple rounds of different and structurally unrelated cancer therapies. However, for some, the concept of multidrug resistance is a worn out idea, stemming from disappointment with the drug resistancereversalstrategiesthatwerecarriedoutinthe1990susingpumpinhibitors to block drug resistance mediated by P-glycoprotein, product of the MDR-1 gene. However, if one takes the larger definition – multidrug resistance as simultaneous resistance to multiple structurally unrelated anticancer therapies – its existence c- not be denied. The purpose of this book is to explore new concepts related to drug resistance in cancer, including resistance to the new molecularly targeted agents. Perhaps new terminology is needed for resistance that occurs following therapy with the targeted agents: Novel Targeted Agent Resistance (NTR). Alternatively, we can return to the original definition of multi drug resistance as simply the resistance to multiple agents that occurs in the course of normal cancer progression.This resistance is likely to be mediated by many factors.
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