New concepts for phase I trials: evaluating new drugs combined with radiation therapy.

The rationale for delivering concomitant chemoradiation is not only to increase tumor cell kill but also to achieve a synergistic effect of chemotherapy and radiation. Combination of chemotherapy and radiotherapy has yielded encouraging results in patients with locally advanced diseases. Our increased knowledge of cancer at the molecular level has transformed our understanding of tumor radiation resistance. Preclinical models have shown that several biologic agents designed to target specifically these molecular processes are radiosensitizing agents. Many of these agents are in the process of clinical evaluation with radiotherapy. The translation of these findings into the clinical setting will be feasible only if early phase I trials demonstrate their safety when combined with ionizing radiation. The combination of new drugs and radiation might not necessarily be equivalent to the toxicity of the new drug plus the usual toxicity of radiation. The doses and schedule to be explored for the new drug might vary from those assessed for the new drug alone. Inappropriate evaluation of a combination regimen can result in unjustified abandonment of a combination, or adoption of a regimen at toxic dose levels because of poor toxicity monitoring. Beside the 'in field' radiation dose-dependent symptoms, 'outside the field' symptoms that are not dose dependent might be identified. Specific and long-term clinical evaluation will be required to identify potentially harmful interactions. It will be necessary to rethink phase I strategies, toxicity endpoints, and trial designs and concepts in order to fully optimize these regimens.