The predictive value of CA125 for ovarian cancer in General Practice: a population-based cohort study of over 50,000 women


Session type:

Garth Funston1,Willie Hamilton2,Gary Abel2,Emma Crosbie3,Brian Rous4,Fiona Walter1

1Department of Public Health and Primary Care, University of Cambridge,2University of Exeter,3Gynaecological Oncology Research Group, Division of Cancer Sciences, University of Manchester,4National Cancer Registration and Analysis Service, Public Health England



The serum biomarker Cancer Antigen 125 (CA125) is recommended for use in UK General Practice (GP) to investigate women presenting with symptoms of possible ovarian cancer. However, no large studies have evaluated its diagnostic performance in this setting. We calculated the predictive value of CA125 for ovarian cancer in English GP.


Women in England with a CA125 recorded in the UK Clinical Practice Research Datalink between the 1st of May 2011 to the 31st of December 2014 were included. Ovarian cancers diagnosed in the 12 months following testing were identified from the cancer registry. We calculated the probability of having ovarian cancer given a CA125 at or above a set cut-off (threshold PPV) and the probability of having ovarian cancer given a specific CA125 level (point PPV) for women >50 and <50 years old. The threshold PPV was calculated for the National Institute of Health and Clinical Excellence (NICE) recommended CA125 cut-off (>35 U/ml). Point PPVs were calculated for each CA125 value up to 1000 U/ml using logistic regression.


50,780 women underwent CA125 testing; 456 (0.9%) were diagnosed with ovarian cancer. The incidence of ovarian cancer was three times higher in women >50 years (0.12%) than in women <50 years (0.4%). Applying the >35U/ml cut-off, CA125 had a threshold PPV of 15.2% (95% CI: 13.6-16.8) in women >50 years and 3.4% (95% CI: 2.5-4.4) in women <50 years. A CA125 level of exactly 41 U/ml in women >50 years and 76 U/ml in women <50 years equated to an ovarian cancer point PPV of 3%- the threshold at which NICE advocates urgent cancer investigation or referral.


CA125 is useful test for ovarian cancer in GP, especially in women >50 years old. Our results can be used by patients and clinicians to determine the estimated probability of having ovarian cancer at any CA125 level, which could help guide decisions on the need for further investigation or referral.