The role of hypoxia in canine cancer.

Human oncology has clearly demonstrated the existence of hypoxic tumours and the problematic nature of those tumours. Hypoxia is a significant problem in the treatment of all types of solid tumours and a common reason for treatment failure. Hypoxia is a negative prognostic indicator of survival and is correlated with the development of metastatic disease. Resistance to radiation therapy and chemotherapy can be because of hypoxia. There are two dominant types of hypoxia recognized in tumours, static and intermittent. Both types of hypoxia are important in terms of resistance. A variety of physiological factors cause hypoxia, and in turn, hypoxia can induce genetic and physiological changes. A limited number of studies have documented that hypoxia exists in spontaneous canine tumours. The knowledge from the human literature of problematic nature of hypoxic tumours combined with the rapid growth of veterinary oncology has necessitated a better understanding of hypoxia in canine tumours.