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Tumor cells exploit their microenvironment by growth factors and cytokines such as vascular endothelial growth factor (VEGF) to stimulate abnormal vessel formation that is leaky and tortuous, causing irregular blood flow. The combination of poor perfusion, raised interstitial fluid pressure and areas of vascular collapse leads to hypoxia within tumor. The latter activates factors such as hypoxia inducible factor 1 (HIF-1) that serve to make cancer cells more aggressive and also markedly influences the response of malignant tumors to conventional irradiation and chemotherapy. Accumulating data now suggest that blockade of oncogenic signaling, for example by PI3K/Akt/mTOR inhibitors, might consist a promising strategy since these agents do not only possess antitumor effects but can also alter tumor vasculature and oxygenation to improve the response to radiation and chemotherapy. In many cases, these changes are related to downregulation of HIF-1α and VEGF. Here, we review the pathophysiology of tumor microenvironment (TME) and how it adversely affects cancer treatment. The complex interaction of tumor vasculature and radiotherapy is examined together the preclinical evidence supporting a proinvasive/metastatic role for ionising radiation. We will discuss the expanding role of oncogenic signaling, especially PI3K/Akt/mTOR, on tumor angiogenesis. Special emphasis will be paid to the potential of different oncogenic pathways blockade and other indirect antivascular strategies to alter the TME for the benefit of cancer treatment, as an alternative to the classical angiogenetic treatment.

Original publication

DOI

10.1007/s10555-012-9394-4

Type

Journal article

Journal

Cancer Metastasis Rev

Publication Date

12/2012

Volume

31

Pages

823 - 842

Keywords

Angiogenesis Inhibitors, Animals, Cell Hypoxia, Humans, Neoplasm Invasiveness, Neoplasm Metastasis, Neoplasms, Neovascularization, Pathologic, Phosphatidylinositol 3-Kinases, TOR Serine-Threonine Kinases, Tumor Microenvironment, Vascular Endothelial Growth Factor A