Cancer antigen 125. The cancer antigen 125 (CA 125) test uses an antibody against antigen from tissue culture of an ovarian tumor cell line. Various published evaluations report sensitivity of about 75%–80% in patients with ovarian carcinoma. There is also an appreciable incidence of elevated values in nonovarian malignancies and in certain benign conditions (see the box on this page). Test values may transiently increase during chemotherapy.
CA 125 has been advocated to monitor patients for recurrence of ovarian carcinoma after initial surgery, similar to the use of CEA after surgery for colon carcinoma. With both CA 125 and CEA there are sufficient normal results (at least 20%) in patients with cancer and sufficient abnormal results in other tumors and in benign conditions to preclude use of the test to screen for tumor under most circumstances. Studies in patients after therapy showed that up to 90% of patients with persistent CA 125 level elevation after surgery had residual tumor, and that nearly all patients with rising titers had recurrent disease; but 50%–61% of patients with normal levels also had recurrent or persistent tumor. Therefore, only a change from normal to abnormal or a rising titer is significant. In one study an increase in titer preceded clinical evidence of metastasis or recurrence by an average of 3 months (range, 1-11 months). CA 125 has also been useful to detect ovarian cancer cells in effusions. However, a study based on decision analysis methodology concluded that CA 125 (and ultrasound) were not cost effective as early detection screening tests for ovarian cancer.

Elevated CA 125 Levels in Various Conditions
Malignant
Epithelial ovarian carcinoma, 75%–80% (range, 25%–92%, better in serous than mucinous cystadenocarcinoma)
Endometrial carcinoma, 25%–48% (2%–90%)
Pancreatic carcinoma, %
Colorectal carcinoma, 20% (15%–56%)
Endocervical adenocarcinoma, %
Squamous cervical or vaginal carcinoma, 7%–14%
Lung carcinoma, 32%
Breast carcinoma, 12%–40%
Lymphoma, 35%
Benign
Cirrhosis, 40%–80%
Acute pancreatitis, 38%
Acute peritonitis, 75%
Endometriosis, 88%
Acute pelvic inflammation disease, 33%
Pregnancy 1st trimester, 2%–24%
During menstruation (occasionally)
Renal failure (? frequency)
Normal persons, 0.6%–1.4%