The maintenance of oxygen homeostasis is required both in physiological dev
elopment and tumour growth. Hypoxia inducible factor (HIF) plays a central
role in both processes. Reliable methods for visualising HIF a subunits hav
e established that HIF activation occurs in the majority of common cancers.
This occurs both by genetic mechanisms and through microenviromental hypox
ia. Activation of the HIF pathway has important effects on patterns of gene
expression in tumours.