HIF1A and cancer: Tissue based biomarkersTechnique: Nitroimidazole compounds, such as pimonidazole, are given systemically and are changed into protein adducts in hypoxic cells. Detectable in biopsies through IHCBenefits: Provides an estimate of hypoxia heterogeneity in different cancer regionsDrawbacks: Indirect measurement of O2 concentrations. Invasive procedure (biopsy required). May not distinguish intermediate hypoxic phenotypes (HIF-1 stabilization occurs at higher O2 levels than that at which adducts are formed). Real-time measurements are not possible