title: Hypoxia in head and neck cancer: how much, how important?
abstract: BACKGROUND
  Hypoxia develops in tumors because of a less ordered, often chaotic, and leaky vascular supply compared with that in normal tissues. In preclinical models, hypoxia has been shown to be associated with treatment resistance and increased malignant potential. In the clinic, several reports show the presence and extent of tumor hypoxia as a negative prognostic indicator. This article reviews the biology and importance of hypoxia in head and neck cancer.
  
  
  METHODS
  A review of literature was carried out and combined with our own experience on hypoxia measurements using exogenous and endogenous markers.
  
  
  RESULTS
  Hypoxia can increase resistance to radiation and cytotoxic drugs and lead to malignant progression, affecting all treatment modalities, including surgery. Hypoxia measurements using electrodes, exogenous bioreductive markers, or endogenous markers show the presence of hypoxia in most head and neck cancers, and correlations with outcome, although limited, consistently indicate hypoxia as an important negative factor. Each hypoxia measurement method has disadvantages, and no "gold standard" yet exists. Distinctions among chronic, acute, and intermediate hypoxia need to be made, because their biology and relevance to treatment resistance differ. Reliable methods for measuring these different forms in the clinic are still lacking. Several methods to overcome hypoxia have been tested clinically, with radiosensitizers (nimorazole), hypoxic cytotoxins (tirapazamine), and carbogen showing some success. New treatments such as hypoxia-mediated gene therapy await proper clinical testing.
  
  
  CONCLUSIONS
  The hypoxia problem in head and neck cancer needs to be addressed if improvements in current treatments are to be made. Increased knowledge of the molecular biology of intermediate, severe, and intermittent hypoxia is needed to assess their relevance and indicate strategies for overcoming their negative influence.
authors.affiliation: Division of Experimental Therapy, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
authors.forename: H L
authors.initials: HL
authors.lastname: Janssen
authors.forename: K M
authors.initials: KM
authors.lastname: Haustermans
authors.forename: A J
authors.initials: AJ
authors.lastname: Balm
authors.forename: A C
authors.initials: AC
authors.lastname: Begg
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use; D014408:Biomarkers, Tumor; D015687:Cell Hypoxia / Q000502:physiology / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D019008:Drug Resistance, Neoplasm / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D006258:Head and Neck Neoplasms / Q000175:diagnosis / Q000503:physiopathology* / Q000628:therapy; D006801:Humans; D006931:Hyperbaric Oxygenation / Q000379:methods; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology; D010100:Oxygen / Q000378:metabolism*; D011379:Prognosis; D016032:Randomized Controlled Trials as Topic; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D014157:Transcription Factors; D010100:Oxygen