The clinical evaluation of cancer chemoprevention agents: defining and contrasting phase I, II, and III objectives.

A number of potential chemoprevention agents are now in clinical trials to evaluate their efficacy. A larger number of compounds await clinical investigation. The design of phase I and phase II trials for cancer chemoprevention agents requires a different approach than for cytotoxic agents. The unique nature of the target populations, the scope of side effect evaluation, and the potential duration of treatment must be considered in the design of these trials. This article will discuss the effect these variables have on the evaluation of a chemoprevention agent and propose models for the phase I and phase II trials of chemoprevention agents.