Poor microenvironmental conditions are a characteristic feature of solid
tumors. Such conditions occur because the
tumor vascular supply, which develops from the normal host vasculature by the process of angiogenesis, is generally inadequate in meeting the
oxygen and nutrient demands of the growing
tumor mass. Regions of low oxygenation (
hypoxia) is believed to be the most critical deficiency, since it has been well documented to play a significant role in influencing the response to conventional radiation and
chemotherapy treatments, as well as influencing malignant progression in terms of aggressive growth and recurrence of the primary
tumor and its metastatic spread. As a result, significant emphasis has been placed on finding clinically applicable approaches to identify those
tumors that contain
hypoxia and realistic methods to target this
hypoxia. However, most studies consider
hypoxia as a single entity, yet we now know that it is multifactorial. Furthermore,
hypoxia is often associated with other microenvironmental parameters, such as elevated interstitial fluid pressure, glycolysis, low pH, and reduced bioenergetic status, and these can also influence the effects of
hypoxia. Here, we review the various aspects of
hypoxia, but also discuss the role of the other microenvironmental parameters associated with
hypoxia.