Mechanisms and clinical significance of multidrug resistance.

Tumor cells often become refractory to diverse drugs with different mechanisms of cytotoxic action. This paper reviews the current state of our knowledge of multidrug resistance, the limitations of present concepts to fully explain the diversity of the MDR phenotypes, and the clinical relevance of these studies derived largely from cell culture systems. The authors discuss the use of markers associated with the multi-drug resistance phenotype to identify potentially drug-resistant tumors and outline strategies that might be used to overcome the resistance phenomenon.