ABSTRACT
In the context of radiobiology, the term ‘‘tumor environment’’ is usually equated with tumor hypoxia. In fact, the presence of foci of low oxygen tension in solid tumors has multiple consequences for tumor progression and treatment outcome, some of which are only recently being explored. The realization that human tumors contained viable cells that were radiobiologically hypoxic, and consequently refractory to radiation treatment, had a massive impact on the practice and development of radiation oncology and focused the attention of clinicians and researchers almost exclusively on the problem of hypoxia formany years. In fact, the solid tumor is an environment in which a number of physiological andmetabolic factors combine to create a unique environment, one aspect of which, albeit a very important one, is hypoxia.
