Multidrug resistance in non-small-cell lung cancer.

Resistance to cytotoxic drugs is an important cause of treatment failure. The causes are complex and may be determined by a combination of the tumour characteristics, such as the proportion of resting cells, adequacy of blood supply, and specific cellular mechanisms, as in the multidrug resistance phenotype. In lung cancer four types of multidrug resistance have been defined on the basis of the cellular drug targets involved, i.e., classical multidrug resistance (MDR), non-P-glycoprotein MDR (also called MRP), atypical MDR (mediated through altered expression of topoisomerases II) and lung resistance-related protein. In lung cancer the role of the different forms of multidrug resistance is complex and only partially understood.