The study of tumour resistance to anticancer drugs has been the subject of many publications since the initial discovery of the phenomenon by J. H. Burchenal and colleagues in 1950. Many papers have been published since then reporting development of resistance to most of the well-known anticancer agents in many different animal tumour systems, both in vivo and in vitro. Many different mechanisms of resistance have been described, and it is clear that the tumour cell has a wide diversity of options in overcoming the cell-killing activity of these agents. Definition of the magnitude of the...