The Ovarian Cancer Marker
CA-125 is a protein found on the surface of ovarian cancer cells and some normal tissues. It's the most widely used ovarian cancer marker, but it's frustratingly nonspecific—endometriosis, fibroids, pelvic inflammatory disease, menstruation, pregnancy, and even liver disease can elevate it. Its best use is MONITORING known ovarian cancer, not screening.
What is CA-125?
CA-125 (cancer antigen 125) is a mucin-type glycoprotein expressed on coelomic epithelium. Normal: <35 U/mL. Elevated in ~80% of advanced ovarian cancers but only ~50% of stage I. Very nonspecific in premenopausal women. Best for monitoring, not screening.
↑ What High CA-125 Means
In a postmenopausal woman with a pelvic mass: very concerning for ovarian cancer. In a premenopausal woman: much more likely to be endometriosis, fibroids, or other benign causes. CA-125 >200 with a complex pelvic mass in a postmenopausal woman is highly suspicious.
Common symptoms:
Often asymptomatic early (ovarian cancer is "the silent killer") · Bloating, pelvic pain, difficulty eating, urinary frequency · Advanced: ascites, weight loss, bowel obstruction
↓ What Low CA-125 Means
Reassuring in the context of ovarian cancer surveillance. Doesn't exclude early-stage ovarian cancer.
Common symptoms:
No symptoms
Why It Matters
When normal:
Monitors ovarian cancer treatment response and recurrence
Helps evaluate pelvic masses (especially postmenopausal)
ROMA (Risk of Ovarian Malignancy Algorithm) combines CA-125 + HE4 for better specificity
Risks if abnormal:
Not recommended for general screening (USPSTF)
Very nonspecific in premenopausal women
Normal CA-125 doesn't exclude early ovarian cancer
Many benign causes of elevation
What Can Cause Abnormal Levels?
Ovarian Cancer
30% likelyElevated in 80% of advanced ovarian cancer. Better marker in postmenopausal women.
Endometriosis
35% likelyVery common benign cause of CA-125 elevation in premenopausal women.
Menstruation
CA-125 fluctuates with the menstrual cycle—higher during menses.
Pelvic Inflammatory Disease
Peritoneal inflammation elevates CA-125.
Fibroids
Uterine fibroids mildly elevate CA-125.
Liver Disease/Ascites
Peritoneal fluid and liver disease elevate CA-125.
Other Cancers
Endometrial, fallopian tube, peritoneal, pancreatic, lung, breast.
What You Can Do
CA-125 is not recommended for screening in average-risk women
Impact: Too many false positives—causes unnecessary surgery \u00B7 Timeline: N/A
If mildly elevated in premenopausal woman: likely benign, repeat after period
Impact: Menstruation elevates CA-125 \u00B7 Timeline: 4-6 weeks
If lifestyle changes aren't enough:
ROMA algorithm (CA-125 + HE4) for pelvic mass evaluation
Impact: Better specificity than CA-125 alone \u00B7 Timeline: With mass workup
Pelvic ultrasound if CA-125 elevated in appropriate clinical context
Impact: Evaluates for pelvic pathology \u00B7 Timeline: As indicated
Recommended retest: Cancer monitoring: per treatment protocol. Elevated without cancer: repeat in 4-6 weeks.
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