The problem of applying experimental
tumor studies to clinical
cancer therapy is a complex one. The
radiotherapy literature contains many examples of premature efforts to apply laboratory observations to the clinic, and many examples of failures to adequately consider animal
tumor observations in the design of clinical studies. This review covers three areas: tumor hypoxia, where clinical trials based on animal
tumor data have been conducted with radiosensitizers, hyperbaric
oxygen, and systemic
oxygen carriers; dose fractionation, where current trials of hyperfractionation are based in part on animal
tumor studies; and chemo-
radiotherapy, where clinical trials are only beginning to exploit concepts developed in animal
tumor systems. The use of animal
tumor systems extends past the screening of new agents. Animal
tumor models can be used in
biological, physiological, and pharmacological studies to elucidate the
biological factors influencing the efficacy of therapeutic agents.
Tumor studies can be combined with studies of normal tissues to predict the toxicities to be anticipated in clinical trials, and to assess the potential for therapeutic gain. Animal studies can also provide data which are useful in designing optimal clinical trials of new agents and maximizing the potential for successful clinical application of new approaches. In general, it is not possible to apply specific laboratory data directly to man. To translate, rather than transpose, information from the laboratory to the clinic, the model studies must be directed at evaluating principles, rather than merely quantifying results. Only through studies of mechanisms, by designing experiments to test or refute a hypothesis, will it be possible to apply model studies to man.