Hypoxia, meaning a lack of oxygen, has been associated strongly with a wide range of human
cancers. Hypoxia occurs when tumor growth exceeds the ability of blood vessels to supply the
tumor with oxygenated blood. It is currently understood that hypoxic tumors are more
aggressive. Current methods for measuring hypoxia include invasive procedures such as tissue
biopsy, or insertion of an electrode into the tumor. EF5-PET may be a non-invasive way to
measure tumor hypoxia.