When a new therapeutic procedure, be it either a cytotoxic drug, surgical operation or radiotherapeutic treatment, is introduced into cancer treatment, it generally requires a careful trial involving comparison with a standard or traditional therapy. The introduction of a new drug in cancer therapy is generally a complex matter, and involves several stages of testing. Such agents are identified as potential anticancer drugs on the basis of preclinical screening studies which involve animal tumour models, and the study of the efficacy of drugs on animal and human tumour cells in tissue culture.