CA 125

Diagnostic Use

It is predominantly used in monitoring the treatment and predicting recurrence of ovarian cancer. CA 125 is not suitable as a standalone screening test for diagnosis of ovarian tumours. However, it has a role to play in guiding referral to gynaecology service for further evaluation – see local health pathway for details.

Although more than 80% of advanced epithelial ovarian cancer have raised CA 125, the sensitivity of CA 125 to detect early-stage ovarian cancer is only about 50%. Not all ovarian tumours (especially the non-epithelial types) express CA 125. In younger women, germ cell tumours are more common than epithelial ovarian cancers and markers such as AFP and hCG, may be more useful. In post-menopausal patients, a raised CA 125 above 35 kU/L is more specific for ovarian cancer than in pre-menopausal women.

CA 125 can be raised in non-ovarian malignancies including cancers of the endometrium, colon, breast, lung and pancreas. Peritoneal metastases from different malignancies can also raise its level.

CA 125 can be raised physiologically during normal menstruation (can be up to 60 U/mL) or 1st trimester pregnancy. It can also be raised in non-malignant conditions involving stretching or inflammation of the ovarian, peritoneal, pleural or pericardial lining e.g. in endometriosis, ovarian cysts, fibroid, pelvic inflammatory disease, recent abdominal surgery, peritonitis, cirrhosis with ascites, hypothyroidism, heart failure, pleuritis and pericarditis. While generally higher CA 125 e.g. >200 kU/L is more suspicious for cancers, there is no specific level that can be considered exclusive to malignancy.

Due to potential influence from inter-laboratory and inter-method variation, for serial monitoring purpose recommend testing CA 125 by the same laboratory using the same method.