**1. Introduction**

22 Advances in the Biology, Imaging and Therapies for Glioblastoma

[27] Williams, J.A., Williams, J.R., Xuan, Y., and Dillehay, L.E. Protracted exposure

Invest., 6:255-263, 1998.

radiosensitization of experimental human malignant glioma. Radiation Oncol.

Glioma cells, both within solid tumors and during invasion, exist in surroundings that are subject to a variety of stresses, including metabolic and environmental stresses. Nonetheless, glioma cells survive and can even thrive under hostile conditions, such as hypoxia, nutrient deprivation, and therapeutic regimens. In order to survive, these tumor cells have to find a way to adapt to such an environment by activating certain growth factor and survival pathways while down-regulating cell death mechanisms. In fact, gliomas adapt so well that they not only survive but proliferate by creating a more hospitable environment through new blood vessel formation and dissemination, even as they endure additional stresses along the way. This chapter reviews the basic stresses that glioma cells encounter during the progression of tumor formation and therapeutic interventions.
