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

Our plain-English summary of Plasma osteopontin levels in patients with head and neck cancer and cervix cancer are critically dependent on the choice of ELISA system, by D. Vordermark, H.M. Said, A. Katzer, et al (BMC Cancer, 2006).

The study

• Authors: D. Vordermark, H.M. Said, A. Katzer, T. Kuhnt, G. Hänsgen, J. Dunst, M. Flentje, M. Bache
• Journal: BMC Cancer
• Published: 2006;6:207
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

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.

In plain English

This laboratory study did not look at asbestos exposure and did not report the patients' exposure histories. It compared blood tests for osteopontin, a protein the authors noted has been discussed as a possible sign of pleural mesothelioma in people exposed to asbestos. The authors measured osteopontin in 88 stored plasma samples from radiotherapy patients treated in Halle, Germany, from 1998 to 2000: 34 samples from 11 patients with head and neck cancer and 54 from 12 patients with cervix cancer. Each sample was measured with a newly introduced ELISA kit (assay A) and an older kit (assay B). Across all samples, the median level was 9.8 ng/ml with assay A and 667.0 ng/ml with assay B. In individual samples the older assay's result was between 2.0 and 217.9 times the newer one's, so no single factor could convert one into the other. The two assays' results were still significantly correlated (r = 0.37, p less than 0.05). The authors concluded that osteopontin levels from commercial kits must be interpreted with caution, but that both assays should be similarly able to rank patients.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory comparison of commercial ELISA test kits on stored (archival) plasma samples, with a comparison against published results
• Who was studied: 88 archival citrate plasma samples from patients treated with radiotherapy between December 1998 and May 2000 at the Martin Luther University of Halle, Germany. 34 samples came from 11 patients with head and neck cancer (ten males, one female) and 54 samples from 12 patients with cervix cancer. Samples were collected between 20 days before and 171 days after the start of radiotherapy. Asbestos exposure histories were not reported.
• Exposure: Asbestos exposure was not studied. The comparison was between osteopontin ELISA kits. Assay A was the TiterZyme kit (Assay Designs) introduced in July 2005. Assay B was the older kit, used as the older TiterZyme version (B1) for the cervix cancer samples and as the current IBL kit (B2) for the head and neck cancer samples.
• Main results:
  • For all 88 samples, the median (range) osteopontin level was 9.8 (3.5–189.5) ng/ml with the new assay A and 667.0 (148.8–2095.0) ng/ml with the older assay B. Assay A results were consistently much lower.
  • The factor between assay B and assay A in individual samples ranged from 2.0 to 217.9 (median 74.6, mean 77.1 according to Table 1). The authors found no uniform factor that would allow one assay's result to be calculated from the other's.
  • Results from assay A and assay B were significantly correlated (r = 0.37, p < 0.05, Spearman rank test).
  • The two versions of the older assay gave similar factors compared with assay A: a median factor of 70.3 for B1 in the cervix cancer samples and 76.5 for B2 in the head and neck cancer samples. The authors took this to mean B1 and B2 can be regarded as identical.
  • Median osteopontin levels were similar in head and neck cancer and cervix cancer patients: 10.4 vs. 9.5 ng/ml with assay A, and 650.2 vs 667.0 ng/ml with assay B.
• The authors' conclusion: The authors concluded that plasma osteopontin levels obtained with commercially available ELISA kits must be interpreted with caution, and that kits sold under the same name may differ, which can compromise comparison with published results. Because the old and new assays were significantly correlated, they suggested both should have a similar potential for selecting patients.
• Limitations the authors state:
  • The time points at which samples were taken were not necessarily comparable between the cervix cancer and head and neck cancer patients.
  • The two versions of the older assay (B1 and B2) were not compared against each other on the same samples.

Topics

Medical terms in this study, explained in our Lexicon: Osteopontin, Glycoprotein, Hypoxia, Pleural Mesothelioma.

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