DRUG-RESISTANCE

Chemotherapy cures a minority of adult tumours (e.g. Hodgkin's and non-Hodgkin's lymphoma, acute leukaemia, teratoma) and the majority of childhood tumours. Prolongation of survival by chemotherapy has been shown for small cell lung cancer, ovarian cancer and breast carcinoma (when used as an adjuvant). However, in the majority of solid tumours there is a less than 20% response to chemotherapy and even curable tumours may relapse and become resistant. Resistance may be de novo, acquired as a stable change within the cell, or be rapidly inducible within the cell after drug administration. Several mechanisms have been described including multidrug resistance, glutathione transferases and DNA repair. Understanding these mechanisms may help to improve the therapeutic ratio and develop new approaches.