CA125 is the most widely used tumour marker in ovarian cancer with unsatisfactory sensitivity and specificity especially at early stage. It is quantified by antibody-based immunoassays; however different molecular weight isoforms have been described in the literature which have never been validated by mass spectrometry, potentially affecting the diagnostic accuracy and clinical reliability of the test. In this study, CA125 was detected by Western blot and its identity confirmed by mass spectrometry. Two-dimensional (2D) gel electrophoresis in combination with mass spectrometry revealed that positive Western blot signals up to 500 kDa are most likely false-positive interactions of M11-like and OC125-like antibodies. Fibronectin, identified as one of these false-positive interaction partners, increased the reading for CA125 in a first generation ELISA significantly (p = 0.02). The existence of low-molecular weight isoforms of CA125 is therefore questionable and is most likely reflecting cross-reactivity of the antibodies with other proteins. This would explain the conflicting reports on the molecular structure of CA125 and also the inconsistency of CA125 levels by different ELISAs. Our results are also the first steps towards a mass spectrometric assay for CA125 quantification, which would improve sensitivity and reliability.
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Univ Hosp North Staffordshire, Dept Gynaeoncol, Stoke On Trent, North Staffords, EnglandUniv Hosp North Staffordshire, Dept Gynaeoncol, Stoke On Trent, North Staffords, England
Birkett, Russell
Parry-Smith, William
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Univ Hosp North Staffordshire, Dept Obstet & Gynaecol, Stoke On Trent, North Staffords, EnglandUniv Hosp North Staffordshire, Dept Gynaeoncol, Stoke On Trent, North Staffords, England
Parry-Smith, William
Todd, Richard
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Univ Hosp North Staffordshire, Dept Gynaeoncol, Stoke On Trent, North Staffords, EnglandUniv Hosp North Staffordshire, Dept Gynaeoncol, Stoke On Trent, North Staffords, England
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Univ Penn, Ctr Res Early Detect, Philadelphia, PA 19104 USA
Univ Penn, Cure Ovarian Canc Sch Med, Philadelphia, PA 19104 USAUniv Penn, Ctr Res Early Detect, Philadelphia, PA 19104 USA
Scholler, Nathalie
Urban, Nicole
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Fred Hutchinson Canc Res Ctr, Mol Diagnosis Program, Div Publ Hlth Sci, Seattle, WA 98109 USAUniv Penn, Ctr Res Early Detect, Philadelphia, PA 19104 USA
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Univ Calif Los Angeles, David Geffen Sch Med, Div Gynecol Oncol, Dept Obstet & Gynecol, Los Angeles, CA 90095 USACedars Sinai Med Ctr, Samuel Oschin Comprehens Canc Inst, Womens Canc Res Inst, Los Angeles, CA 90048 USA
Karam, Amer K.
Karlan, Beth Y.
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Cedars Sinai Med Ctr, Samuel Oschin Comprehens Canc Inst, Womens Canc Res Inst, Los Angeles, CA 90048 USACedars Sinai Med Ctr, Samuel Oschin Comprehens Canc Inst, Womens Canc Res Inst, Los Angeles, CA 90048 USA