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Cancer Antigen 125 (CA-125)

This is a surface antigen on a high-molecular weight glycoprotein recognised by a monoclonal antibody (produced using an ovarian cancer cell line).1 It is most useful as a marker for non-mucinous ovarian epithelial cancer2, and indeed is present in up to 80% of cases of advanced ovarian cancer - but is often negative earlier in the disease.3

Conditions which may have elevated CA-125

Malignant Disease

Non malignant conditions

Normal range

CA-125 kU/L <30 (may vary between laboratories).

Uses of CA-125

Monitoring known patients with ovarian cancer for relapse

Three studies have looked at the correlation of CA-125 in patients treated for ovarian cancer who subsequently underwent a second staging operation to look for any persisting disease.7,8,9 Combining the results1, the CA-125 has a sensitivity of 55% and a specificity of 96%, giving a positive predictive value of around 96% and a negative predictive value of 53%. Thus in patients with known ovarian cancer a rising CA-125 is a good indicator of residual disease but a normal result will be a false negative about half the time in this group (not a good indicator of small volume disease).

Investigation of female patients with a pelvic mass

CA-125 can be used in the assessment of patients presenting with a pelvic mass. An elevated result has a sensitivity of 72% and specificity of 78% for ovarian cancer (positive predictive value of 72% and a negative predictive value of 78%).10 If combined ultrasound results and menopausal status, a risk of malignancy index (RMI) can be calculated. Using a cut-off level of CA-125=200 to indicate malignancy, the RMI gave a sensitivity of 90%, specificity of 89%, positive predictive value of 96%, and negative predictive value of 78% in this group.11

Screening for Ovarian Cancer

The relatively low prevalence of ovarian cancer means that the positive predictive value of CA-125 as a screening test is extremely low.12 CA-125 is being evaluated as a screening tool for patients at high risk of ovarian cancer, in combination with other tests. The UK Familial Ovarian Cancer Screening Study (UKFOCSS) is recruiting women with strong family histories or mutations in BRCA1 or BRCA2, to be screened with trans-vaginal ultrasound scan of the ovaries and CA-125 three times a year.13 A second study, the UK Collaborative Trial of Ovarian Cancer Screening (UKCTOCS) study has finished recruiting.14

Document references
  1. William M. Rich, M.D. CA-125 www.gynoncology.com
  2. Kabawat SE, Bast RC, Welch WR, et al; Immunopathologic characterization of a monoclonal antibody that recognizes common surface antigens of human ovarian tumors of serous, endometrioid, and clear cell types. Am J Clin Pathol. 1983 Jan;79(1):98-104. [abstract]
  3. Jacobs I, Bast RC Jr; The CA 125 tumour-associated antigen: a review of the literature. Hum Reprod. 1989 Jan;4(1):1-12. [abstract]
  4. Epithelial Ovarian Cancer, SIGN Guideline No 75 (October 2003)
  5. Moran-Mendoza A, Alvarado-Luna G, Calderillo-Ruiz G, et al; Elevated CA125 level associated with Meigs' syndrome: case report and review of the literature.; Int J Gynecol Cancer. 2006 Jan-Feb;16 Suppl 1:315-8. [abstract]
  6. Lacey JV Jr, Greene MH, Buys SS, et al; Ovarian cancer screening in women with a family history of breast or ovarian cancer. Obstet Gynecol. 2006 Nov;108(5):1176-84. [abstract]
  7. Patsner B, Orr JW Jr, Mann WJ Jr, et al; Does serum CA-125 level prior to second-look laparotomy for invasive ovarian adenocarcinoma predict size of residual disease? Gynecol Oncol. 1990 Sep;38(3):373-6. [abstract]
  8. Petru E, Sevin BU, Averette HE, et al; Comparison of three tumor markers--CA-125, lipid-associated sialic acid (LSA), and NB/70K--in monitoring ovarian cancer. Gynecol Oncol. 1990 Aug;38(2):181-6. [abstract]
  9. Rubin SC, Hoskins WJ, Hakes TB, et al; Serum CA 125 levels and surgical findings in patients undergoing secondary operations for epithelial ovarian cancer. Am J Obstet Gynecol. 1989 Mar;160(3):667-71. [abstract]
  10. Patsner B, Mann WJ; The value of preoperative serum CA 125 levels in patients with a pelvic mass. Am J Obstet Gynecol. 1988 Oct;159(4):873-6. [abstract]
  11. Obeidat BR, Amarin ZO, Latimer JA, et al; Risk of malignancy index in the preoperative evaluation of pelvic masses. Int J Gynaecol Obstet. 2004 Jun;85(3):255-8. [abstract]
  12. Screening for ovarian cancer: a systematic review. Health Technology Assessment 1998; Vol. 2: No. 2 (Executive summary)
  13. Breakthrough - UK Familial Ovarian Cancer Screening Study
  14. UK Collaborative Trial of Ovarian Cancer Screening
Acknowledgements EMIS is grateful to Dr Huw Thomas for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2008.
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Document Version: 22
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Last Updated: 12 Apr 2007
Review Date: 11 Apr 2009




















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PS - Health and Poverty

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