Clinical studies in the development of new anticancer agents exhibiting growth inhibition in models: facing the challenge of a proper study design.

Various new specifically targeted anticancer agents such as matrixmetalloproteinase inhibitors, angiogenesis inhibitors, farnesyl transferase inhibitors, and tyrosine kinase inhibitors have been developed in recent years. These agents exert antitumor activity through specific target inhibition, and preclinical studies showed dose-dependent tumor growth inhibition and only sporadic tumor regressions. Toxicity of these new agents was often strikingly mild or did not occur at all. Clinical studies are now being performed. Because these new agents might have a different toxicity profile and exert their antitumor activity in a way that is completely different from that of cytotoxic agents, the design of clinical studies will have to be adapted in several ways, and new endpoints for phase I, II, and III studies must be defined.