title: Quantification of the concentration gradient of biomarkers between ovarian carcinoma interstitial fluid and blood.
abstract: BACKGROUND
  Tumor interstitial fluid (TIF) rather than plasma should be used in cancer biomarker discovery because of the anticipated higher concentration of locally produced proteins in the tumor microenvironment. Nevertheless, the actual TIF-to-plasma gradient of tumor specific proteins has not been quantified. We present the proof-of-concept for the quantification of the postulated gradient between TIF and plasma.
  
  
  METHODS
  TIF was collected by centrifugation from serous (n = 19), endometrioid (n = 9) and clear cell (n = 3) ovarian carcinomas with early (n = 15) and late stage (n = 16) disease in grades 1 (n = 2), 2 (n = 8) and 3 (n = 17), and ELISA was used for the determination of CA-125, osteopontin and VEGF-A.
  
  
  RESULTS
  All three markers were significantly up-regulated in TIF compared with plasma (p < 0.0001). The TIF-to-plasma ratio of the ovarian cancer biomarker CA-125 ranged from 1.4 to 24,300 (median = 194) and was inversely correlated to stage (p = 0.0006). The cancer related osteopontin and VEGF-A had TIF-to-plasma ratios ranging from 1 to 62 (median = 15) and 2 to 1040 (median = 59), respectively. The ratios were not affected by tumor stage, indicative of more widespread protein expression.
  
  
  CONCLUSIONS
  We present absolute quantitative data on the TIF-to-plasma gradient of selected proteins in the tumor microenvironment, and demonstrate a substantial and stage dependent gradient for CA-125 between TIF and plasma, suggesting a relation between total tumor burden and tissue-to-plasma gradient.
  
  
  CONCLUSIONS
  We present novel quantitative data on biomarker concentration in the tumor microenvironment, and a new strategy for biomarker selection, applicable in future biomarker studies.
authors.affiliation: Department of Biomedicine, University of Bergen, Norway ; Department of Bioprocess Technology, SINTEF Materials and Chemistry, Trondheim, Norway.
authors.forename: Hanne
authors.initials: H
authors.lastname: Haslene-Hox
authors.affiliation: Department of Biomedicine, University of Bergen, Norway.
authors.forename: Amina
authors.initials: A
authors.lastname: Madani
authors.affiliation: Department of Biomedicine, University of Bergen, Norway.
authors.forename: Kaja C G
authors.initials: KC
authors.lastname: Berg
authors.affiliation: Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Kathrine
authors.initials: K
authors.lastname: Woie
authors.affiliation: Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway ; Department of Clinical Medicine, University of Bergen, Bergen, Norway.
authors.forename: Helga B
authors.initials: HB
authors.lastname: Salvesen
authors.affiliation: Department of Biomedicine, University of Bergen, Norway.
authors.forename: Helge
authors.initials: H
authors.lastname: Wiig
authors.affiliation: Department of Biomedicine, University of Bergen, Norway.
authors.forename: Olav
authors.initials: O
authors.lastname: Tenstad
keywords: Biomarker; CA-125; CA-125, cancer antigen 125; EDTA, ethylenediaminetetraacetic acid; FIGO, International Federation of Gynecology and Obstetrics; Ovarian carcinoma; PBS, phosphate buffered saline; TIF, tumor interstitial fluid; Tumor interstitial fluid; Tumor microenvironment