title: Plasma osteopontin levels in patients with head and neck cancer and cervix cancer are critically dependent on the choice of ELISA system.
abstract: BACKGROUND
  The tumor-associated glycoprotein osteopontin (OPN) is discussed as a plasma surrogate marker of tumor hypoxia and as an indicator of the presence of pleural mesothelioma in asbestos-exposed individuals. The clinical introduction of plasma OPN measurements requires the availability of a reliable enzyme-linked immunosorbence assay (ELISA).
  
  
  METHODS
  We compared previously described and currently available ELISA systems on 88 archival plasma samples obtained from patients with head and neck or cervix cancer between 20 days before and 171 after the start of radiotherapy.
  
  
  RESULTS
  Median (range) plasma OPN levels were 667 (148.8-2095) ng/ml and 9.8 (3.5-189.5) ng/ml for a previously described and a newly marketed assay, respectively. Although results for different assays were significantly correlated (r = 0.38, p < 0.05, Spearman rank test), between-assay factors ranged from 2.0 to 217.9 (median 74.6) in individual patients. OPN levels in cervix cancer patients were comparable to those of head and neck cancer patients.
  
  
  CONCLUSIONS
  Commercially available OPN ELISA systems produce different absolute plasma OPN levels, compromising a comparison of individual patient data with published results. However, different assays appear to have a similar capacity to rank patients according to plasma OPN level. A review of literature data suggests that plasma OPN levels measured even with identical ELISA systems can only be compared with caution.
authors.affiliation: Dept. of Radiation Oncology, University of Würzburg, Germany. vordermark_d@klinik.uni-wuerzburg.de
authors.forename: Dirk
authors.initials: D
authors.lastname: Vordermark
authors.forename: Harun M
authors.initials: HM
authors.lastname: Said
authors.forename: Astrid
authors.initials: A
authors.lastname: Katzer
authors.forename: Thomas
authors.initials: T
authors.lastname: Kuhnt
authors.forename: Gabriele
authors.initials: G
authors.lastname: Hänsgen
authors.forename: Jürgen
authors.initials: J
authors.lastname: Dunst
authors.forename: Michael
authors.initials: M
authors.lastname: Flentje
authors.forename: Matthias
authors.initials: M
authors.lastname: Bache
mesh_terms: D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006258:Head and Neck Neoplasms / Q000097:blood*; D006801:Humans; D008297:Male; D053495:Osteopontin; D012795:Sialoglycoproteins / Q000097:blood*; D002583:Uterine Cervical Neoplasms / Q000097:blood*
chemical_list: C506895:SPP1 protein, human; D012795:Sialoglycoproteins; D053495:Osteopontin