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Cancer antigen 125 (CA125)

Category Biochemistry >> Oncology
Test background

CA125 is a coelomic cell-surface glycoprotein of 200 kDa that is expressed on cells of serous ovarian carcinoma. CA125 is defined by the OC125 monoclonal antibody. It is expressed predominantly in ovarian cancer, though primary tumours of the endometrium, fallopian tubes, lung, breast, liver or gastrointestinal tract may also give rise to elevations of serum CA125. Many other conditions aside from ovarian cancer may also cause increased levels, notably: endometriosis, menstruation, pelvic inflammatory disease, pregnancy, chronic hepatitis, congestive heart failure and poorly controlled diabetes. Higher levels (>100 kIU/L), or continuously increasing levels, are more specifically associated with ovarian cancer.

Clinical Indications

Ovarian cancer

Diagnosis: the 2011 NICE guideline established that CA125 testing was the most cost-effective strategy for early diagnosis of ovarian cancer. Screening for ovarian cancer in women at risk or with symptoms should be in combination with other modalities (ie. bimanual pelvic examination, transvaginal ultrasonography). CA125 and ultrasound measurements are used in calculating a risk of malignancy index for distinguishing benign from malignant pelvic masses.

Prognosis: pre- and post-operative CA125 measurements have prognostic value.

Treatment monitoring: baseline samples should be taken within 2 weeks prior to treatment and every 2-4 weeks during treatment. The rate of decline during initial therapy is a strong and independent prognostic indicator of response. A half-life of less than 20 days following chemotherapy correlates improved survival.

Surveillance: elevated or rising levels predict relapse.

Reference range

Female: 0-35 kIU/L

Sample & container required SST (gold top) preferred, serum (red top) accepted
Sample volume 0.5 mL
Turnaround time 4 days

Abbott Alinity