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CA-125 (“Cancer Antigen – 125”) is a protein expressed on the surface of ovarian cells, and other cells (to a lesser extent) around the body.

It is often used as a tumour marker in known cases of ovarian cancer – specifically epithelial ovarian cancer. Various studies have assessed its efficacy as a screening test for ovarian cancer, but have failed to prove its benefit.

  • Some studies which combine CA-125 with pelvic ultrasound as a screening test show some promise, but this is not yet a routine screening test

There are also various other causes for a raised CA-125. It may be requested by alternative health practitioners, and patients with a subsequently elevated result may present to their general practitioner for review of the results.

A “normal” CA-125 is typically in the range of 0-25 units/L

Causes of elevated CA-125

Use in Ovarian Cancer

CA-125 can be used both in the detection of ovarian cancer in symptomatic patients, and the monitoring of treatment for ovarian cancer.

Unfortunately, it has low sensitivity in the early stages (cases of ovarian cancer with normal CA-125 will be missed), and low specificity when elevated (as above – there are lots of causes!).

  • Tumours that have LESS than a 7 fold decrease in CA-125 after chemotherapy carry a worse prognosis
  • It is also used in long-term monitoring when checking for recurrence of ovarian cancer
  • Is only useful for epithelial ovarian carcinoma. Other types of ovarian carcinoma (germ cell tumours) do not reliably produce increased amounts of CA-125. Instead these tumours may be detected by αFP and βHCG

CA-125 is also used in the work-up of woes with suspected ovarian cancer

  • Most guidelines suggest that in a women with symptoms suggestive of ovarian cancer, CA-125 and pelvic ultrasound should be performed
  • Risk of ovarian cancer for women with symptoms of ovarian cancer:
    • Positive USS and positive CA-125 – 1 in 26 have ovarian cancer
      • BUT – using only these criteria 34% of cases are not detected
    • Positive CA-125 OR ultrasound – 1 in 100 have ovarian cancer
    • Negative CA-125 AND ultrasound – 1 in 2000 have ovarian cancer

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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