CA-125

CA-125 (Cancer Antigen 125) is a protein found on the surface of many cells, particularly ovarian cells. When these cells are irritated or damaged — whether by cancer or other conditions — CA-125 is released into the bloodstream. Elevated levels are associated with ovarian cancer, making CA-125 valuable for monitoring treatment and detecting recurrence.

However, CA-125 is not a simple “cancer yes or no” test. Many benign conditions also raise CA-125, including endometriosis, fibroids, pelvic inflammatory disease, and even normal menstruation. This limits its usefulness as a screening test for ovarian cancer in women without symptoms. Where CA-125 truly shines is in monitoring women already being treated for ovarian cancer — tracking whether treatment is working and detecting recurrence early.

Order Your CA-125 Test

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Key Benefits of Testing

CA-125 testing serves several important purposes. For women with known ovarian cancer, it tracks treatment response — falling levels indicate treatment is working, while rising levels may signal recurrence. For women with pelvic masses, CA-125 helps assess whether a mass is more likely benign or malignant, guiding surgical planning.

In specific high-risk populations — particularly women with BRCA mutations or strong family history of ovarian cancer — CA-125 may be part of a surveillance strategy, though its role in screening remains limited by the many non-cancer causes of elevation.

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What Does This Test Measure?

CA-125 measures the concentration of Cancer Antigen 125 protein in blood. This protein is produced by cells lining various body cavities including the ovaries, fallopian tubes, uterus, and peritoneum (abdominal lining). When these tissues are irritated, inflamed, or cancerous, more CA-125 enters the bloodstream.

Sources of CA-125

Source	When CA-125 Rises	Clinical Context
Ovarian cancer	Cancer cells produce excess CA-125	Primary use — monitoring treatment and recurrence
Endometriosis	Endometrial tissue outside uterus causes irritation	Common cause of elevated CA-125 in premenopausal women
Fibroids	Large fibroids can elevate levels	Benign, but can confuse interpretation
Pelvic inflammatory disease	Infection causes inflammation	Temporary elevation that resolves with treatment
Menstruation	Normal shedding of endometrium	Test ideally done after period ends
Pregnancy	Especially first trimester	Normal physiological elevation
Other cancers	Pancreatic, lung, breast, colon	Less specific than for ovarian cancer

Why CA-125 Isn’t a Perfect Screening Test

For a screening test to work well, it needs to be elevated when cancer is present (sensitive) and normal when cancer is absent (specific). CA-125 falls short on both counts for general screening:

Limitation	Explanation	Consequence
Not always elevated in early cancer	About 50% of early-stage ovarian cancers have normal CA-125	Misses many cancers when they’re most treatable
Often elevated without cancer	Endometriosis, fibroids, PID, menstruation all raise it	False alarms leading to unnecessary worry and procedures
Ovarian cancer is relatively rare	Even a “good” test produces many false positives in rare diseases	Most women with elevated CA-125 don’t have ovarian cancer

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Why This Test Matters

Monitoring Ovarian Cancer Treatment

This is where CA-125 is most valuable. In women with ovarian cancer that produces CA-125 (not all do), the level serves as a real-time indicator of how well treatment is working:

• Falling CA-125 during chemotherapy — Treatment is working, cancer is responding
• CA-125 returns to normal — Good response, though doesn’t guarantee cure
• Rising CA-125 during or after treatment — Cancer may be progressing or recurring

Tracking CA-125 allows doctors to adjust treatment strategies and catch recurrence months before symptoms or imaging changes would appear.

Evaluating Pelvic Masses

When imaging discovers a pelvic mass, CA-125 helps assess the likelihood of malignancy:

Patient Profile	CA-125 Result	Interpretation
Postmenopausal woman	Elevated	Higher concern for malignancy — referral to gynecologic oncologist
Postmenopausal woman	Normal	Lower concern, but doesn’t rule out cancer
Premenopausal woman	Elevated	May be endometriosis, fibroids, or other benign causes — context matters
Premenopausal woman	Normal	Benign cause more likely

High-Risk Surveillance

Women at significantly increased risk for ovarian cancer — particularly those with BRCA1 or BRCA2 mutations — face difficult decisions about surveillance versus preventive surgery. While CA-125 combined with transvaginal ultrasound is sometimes used for monitoring, this approach has not been proven to reduce ovarian cancer deaths. Many high-risk women ultimately choose risk-reducing surgery (removal of ovaries and fallopian tubes) rather than ongoing surveillance.

Value of Testing When Evaluating Symptoms

Ovarian cancer is called “the silent killer” because early symptoms are vague — bloating, pelvic discomfort, feeling full quickly, urinary frequency. These symptoms are common and usually from benign causes. However, when symptoms are new, persistent (present most days for more than a few weeks), and represent a change from baseline, evaluation is warranted. CA-125, combined with pelvic examination and imaging, helps assess whether symptoms might represent something serious. Testing provides objective information that guides next steps — offering either reassurance or early detection of problems.

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What Can Affect CA-125 Levels?

Conditions That Raise CA-125

Gynecologic conditions:

• Ovarian cancer (primary concern)
• Endometriosis (very common cause in premenopausal women)
• Uterine fibroids
• Pelvic inflammatory disease
• Ovarian cysts
• Adenomyosis

Other cancers:

• Fallopian tube cancer
• Primary peritoneal cancer
• Endometrial cancer
• Pancreatic, lung, breast, colon cancer (less consistently)

Non-gynecologic conditions:

• Liver cirrhosis
• Ascites (fluid in abdomen) from any cause
• Pleural effusion
• Heart failure
• Recent abdominal surgery

Normal physiological states:

• Menstruation
• Pregnancy (especially first trimester)

Testing Considerations

Timing: In premenopausal women, CA-125 can fluctuate with the menstrual cycle. Testing is ideally done after menstruation ends to avoid false elevation.

Trends matter: A single CA-125 value is less informative than the trend over time. Rising values are more concerning than a single elevated result that remains stable.

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When Should You Get Tested?

Established Indications

• Monitoring known ovarian cancer — Track treatment response and detect recurrence
• Evaluating a pelvic mass — Help assess likelihood of malignancy, especially in postmenopausal women
• Persistent unexplained symptoms — New, persistent bloating, pelvic pain, difficulty eating, urinary symptoms warranting evaluation

Possible Indications (Discuss with Your Doctor)

• High-risk women (BRCA mutations, strong family history) — May be part of surveillance strategy, though limitations exist
• Monitoring endometriosis — Sometimes used to track disease activity

Not Recommended For

• Routine screening in average-risk women — Studies have not shown benefit, and false positives cause harm
• Annual “just to check” testing — Without symptoms or risk factors, not recommended

Order Your Test

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Understanding Your Results

Interpreting CA-125

Results are reported as units per milliliter (U/mL). The reference range typically considers values below a certain threshold as normal, but interpretation depends heavily on clinical context.

Result Category	In Postmenopausal Women	In Premenopausal Women
Normal range	Reassuring but doesn’t exclude early cancer	Reassuring, cancer unlikely
Mildly elevated	Warrants further evaluation	Often benign (endometriosis, fibroids, etc.)
Moderately elevated	Concerning, imaging and possible referral needed	Context-dependent, may be benign or concerning
Highly elevated	High suspicion for malignancy	Concerning, needs evaluation

Context Is Everything

The same CA-125 value can mean different things in different women:

• Mildly elevated in a 30-year-old with known endometriosis — likely related to endometriosis
• Mildly elevated in a 65-year-old with a pelvic mass — more concerning for malignancy
• Falling from high levels in a woman on chemotherapy — good treatment response
• Rising in a woman previously treated for ovarian cancer — possible recurrence

Trends Over Time

Serial measurements are often more informative than single values:

• Stable mildly elevated — Less concerning than rising values
• Steadily rising — Warrants investigation regardless of absolute level
• Falling during treatment — Positive response
• Rising after treatment — Possible recurrence, often detected months before symptoms

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What to Do About Your Results

If CA-125 Is Normal

A normal result is reassuring but has limitations. About half of early-stage ovarian cancers don’t elevate CA-125. If concerning symptoms persist despite normal CA-125, further evaluation may still be warranted. Normal CA-125 in a woman being monitored after ovarian cancer treatment is a good sign.

If CA-125 Is Elevated

Don’t panic. Elevated CA-125 does not mean you have cancer. In premenopausal women especially, benign causes are far more common.

Next steps typically include:

• Review of symptoms and medical history
• Pelvic examination
• Pelvic ultrasound (transvaginal is most informative)
• Possibly repeat CA-125 to assess trend
• Referral to gynecologist or gynecologic oncologist depending on findings

If You’re Being Monitored for Ovarian Cancer

Your oncology team will interpret CA-125 trends in the context of your treatment. Generally:

• Falling levels — Continue current treatment approach
• Rising levels — May prompt imaging or treatment changes
• The trend and rate of change often matter more than absolute numbers

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Related Health Conditions

Ovarian Cancer

Ovarian cancer is the most serious condition associated with elevated CA-125. Most cases are diagnosed at advanced stages because early symptoms are vague. CA-125 is primarily used for monitoring treatment response and detecting recurrence rather than initial screening. Treatment typically involves surgery and chemotherapy.

Endometriosis

Endometriosis occurs when tissue similar to the uterine lining grows outside the uterus. It commonly elevates CA-125, making interpretation challenging in premenopausal women. Symptoms include painful periods, pelvic pain, and infertility. CA-125 is sometimes used to monitor disease activity.

Ovarian Cysts

Most ovarian cysts are benign and resolve on their own. CA-125 helps assess whether a cyst is more likely benign or concerning for malignancy, particularly in postmenopausal women where benign functional cysts are less common.

Uterine Fibroids

Fibroids are benign uterine tumors that can elevate CA-125, especially when large. They cause symptoms like heavy bleeding and pelvic pressure but are not cancerous.

Pelvic Inflammatory Disease

PID is infection of the female reproductive organs, usually from sexually transmitted bacteria. It can significantly elevate CA-125. Levels return to normal after successful treatment.

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Related Biomarkers Often Tested Together

HE4 (Human Epididymis Protein 4) — Another ovarian cancer marker, often combined with CA-125 in the ROMA score to better assess ovarian cancer risk in women with pelvic masses.

CEA (Carcinoembryonic Antigen) — Tumor marker that can help distinguish ovarian cancer type and detect other cancers that may spread to ovaries.

AFP (Alpha-Fetoprotein) — Elevated in certain ovarian germ cell tumors, useful in younger women with ovarian masses.

LDH (Lactate Dehydrogenase) — Non-specific marker that can be elevated in ovarian germ cell tumors.

Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.