Oxygen and cancer.

: Tumor hypoxia results from multiple pathophysiologic interactions. Abnormalities in tumor vessel structure and function lead to decreased oxygen delivery relative to normal tissue. Furthermore, a relatively high rate of tumor cell proliferation increases oxygen consumption by tumor tissue. The net result of decreased oxygen supply and increased oxygen demand is hypoxia. Hypoxia makes tumors resistant to radiation and some chemotherapy, and it induces expression of growth factors, angiogenic factors, and cell cycle regulatory proteins that affect tumor phenotype. Recent attempts to make tumors more sensitive to radiation and chemotherapy by reducing hypoxia (by increasing tumor blood flow, the use of oxic gases, and blood substitutes) have been ineffective. Future research may be directed more toward decreasing oxygen consumption or actually exploiting the hypoxic environment to achieve a therapeutic benefit.