Fundamental bases of combined therapy in lung cancer: cell resistance to chemotherapy and radiotherapy.

This overview briefly examines the mechanisms of drug resistance in lung cancer, including multidrug resistance and its atypical phenotypes, the role of cytoplasmic protectors such as glutathione, and resistance at the level of the DNA through topoisomerases, gene amplification or mutation, and DNA repair. Understanding of radioresistance is less advanced, but resistance may arise through limitation of the amount of DNA damage inflicted or by its subsequent modification by intracellular protectors or DNA repair. The mechanisms of radioresistance are generally distinct from those of chemoresistance providing a rationale for the use of combined modality therapy.