HIF1A and neoplasm: Hypoxia can also be intermittent which can add complexity to any interpretation, especially when coupled with differences in oxygen saturation within different regions of the tumour microenvironment.29–31 HIF-1α serves as an important sensor and regulator of cellular oxygen levels; it protects cells from undergoing apoptosis under hypoxic conditions as well as promoting glycolysis alongside corresponding decreases in mitochondrial oxidative phosphorylation in cancer cells (an effect known as the Warburg effect;  See Box 2).