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Open Access Research article

Plasma osteopontin levels in patients with head and neck cancer and cervix cancer are critically dependent on the choice of ELISA system

Dirk Vordermark1*, Harun M Said1, Astrid Katzer1, Thomas Kuhnt2, Gabriele Hänsgen2, Jürgen Dunst23, Michael Flentje1 and Matthias Bache2

Author Affiliations

1 Dept. of Radiation Oncology, University of Würzburg, Germany

2 Dept. of Radiation Oncology, Martin Luther University of Halle, Germany

3 Dept. of Radiation Oncology, University of Lübeck, Germany

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BMC Cancer 2006, 6:207  doi:10.1186/1471-2407-6-207

Published: 15 August 2006

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.

Conclusion

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.