CA125 is the most widely used tumour marker for epithelial ovarian cancer.

• It is used in the differential diagnosis of ovarian cysts and pelvic masses in postmenopausal women. CA125 should be used in conjunction with transvaginal ultrasound scans (TVUS) for the calculation of the Risk of Malignancy Index (RMI)

• It is measured in patients with ovarian cancer to assess response to chemotherapy and to detect tumour recurrence.

• Since the NICE guidelines for the early recognition of ovarian cancer were published in April 2011, it is now recommended that individuals who present in primary care with symptoms suggestive of ovarian cancer have a CA125 measurement, to determine the need for further investigations including pelvic and abdominal ultrasound scans.

• It is used to screen women with a family history of hereditary forms of ovarian cancer.

• CA125 should not be used for screening asymptomatic women.

Patients on high dose biotin therapy (>5mg/day) samples need to be at least 8 hours after the last dose.