Development of target-based antineoplastic agents.

The elucidation of multiple potential targets in cancer cells and the development of multiple target-based antineoplastic agents provide unique challenges in clinical trial design. Many of these agents are predicted to have cytostatic as opposed to cytotoxic effects and thus the traditional surrogate endpoint of radiologic tumor shrinkage may be inadequate. The ethical and safety issues of obtaining multiple tumor biopsies further complicate the assessment of appropriate target inhibition in patients. We discuss specific issues that need to be addressed during preclinical, phase I, II, and III testing of these agents. We propose clinical trial designs, including a randomized discontinuation design during phase II evaluation, that may be particularly useful for cytostatic antineoplastic agents.