Overview
CA15-3 (Cancer Antigen 15-3) is a protein (tumor marker) that is mainly associated with breast cancer. It is not used for screening or early diagnosis but plays a crucial role in monitoring treatment response, detecting recurrence, and identifying metastatic spread (cancer that has spread to other organs).
CA15-3 levels are measured through a simple blood test, and high levels may indicate the presence or progression of certain cancers, especially advanced breast cancer. However, mild elevations can also occur in non-cancerous (benign) conditions.
What is CA15-3?
CA15-3 is a glycoprotein (a protein with sugar molecules attached) that is found on the surface of epithelial cells, particularly in the mammary glands (breast tissue).
When cancer develops in these cells, especially in breast carcinoma, more CA15-3 is released into the bloodstream.
Doctors measure CA15-3 levels to:
- Monitor the effectiveness of treatment
- Detect recurrence
- Assess cancer spread to other organs (metastasis)
It is important to note that CA15-3 is not used for early detection because it may remain normal in early-stage breast cancer or increase in other conditions unrelated to cancer.
Where is CA15-3 Produced in the Body?
CA15-3 is primarily produced by epithelial cells of the mammary glands (breast tissue). However, smaller amounts may also be produced by other glandular tissues in the body, such as:
- Lungs
- Ovaries
- Pancreas
- Liver
In breast cancer, particularly metastatic breast cancer, cancerous cells shed larger quantities of CA15-3 into the bloodstream, making it detectable through a blood test.
Main Functions and Importance
Although CA15-3 does not serve a biological function in normal body processes, it has significant clinical importance in cancer diagnosis and follow-up.
1. Breast Cancer Monitoring
- The primary use of CA15-3 is to track disease progression and monitor treatment response in patients with known breast cancer.
- A decrease in CA15-3 levels indicates effective therapy, while a rise may signal recurrence or metastasis.
2. Metastatic Disease Detection
- Helps identify whether breast cancer has spread to other organs, especially the bones, liver, or lungs.
3. Not for Early Detection
- CA15-3 has low sensitivity in early-stage breast cancer, meaning it often remains normal even when the disease is present.
- Therefore, it is not suitable as a screening test for healthy individuals.
4. Combined Testing
- CA15-3 is sometimes measured along with CA27.29 or used in combination with imaging methods like mammography, ultrasound, or MRI for more accurate results.
Causes of Low or Normal CA15-3 Levels
Low CA15-3 Levels
- Normal or low CA15-3 levels are common in healthy people.
- In breast cancer patients, low or decreasing levels after treatment indicate a good response and possible remission (disease under control).
Symptoms of Low CA15-3
- There are no symptoms associated with low CA15-3 levels.
- It usually means the person is healthy or the cancer is responding well to therapy.
Causes of High CA15-3 Levels (Elevated CA15-3)
CA15-3 can rise in both cancerous and non-cancerous conditions.
Cancer-Related Causes
- Breast cancer (especially advanced or metastatic)
- Lung cancer
- Ovarian cancer
- Pancreatic cancer
- Liver cancer
Non-Cancerous (Benign) Causes
- Liver diseases such as cirrhosis or hepatitis
- Benign breast conditions (fibrocystic breast disease, mastitis)
- Endometriosis (uterine tissue growing outside the uterus)
- Pelvic inflammatory disease (PID)
- Pregnancy and lactation (mild, temporary rise possible)
Symptoms of High CA15-3 Levels
High CA15-3 itself does not cause symptoms. However, if the underlying cause is cancer or another disease, symptoms may include:
- Breast lumps or thickening
- Breast pain or tenderness
- Changes in breast skin or nipple appearance
- Unexplained weight loss or fatigue
- Bone pain (if cancer has spread to bones)
- Jaundice or abdominal discomfort (if spread to the liver)
If these symptoms appear, medical evaluation and imaging studies are recommended.
Reference Range (Normal Blood Levels)
| Level Category | CA15-3 (U/mL) | Interpretation |
|---|---|---|
| Normal | < 30 U/mL (some labs use <25 U/mL) | Normal or healthy |
| Mild Elevation | 30–100 U/mL | May indicate benign or early malignant condition |
| High Elevation | > 100 U/mL | Often linked to metastatic or advanced breast cancer |
Note: A high value must always be correlated with imaging tests and clinical findings before concluding cancer recurrence.
Sample Type and Test Details
- Sample Type: Blood (Serum)
- Tube Used: Red Top (Plain Tube)
- Fasting Required: No
- Report Time: Usually 1–2 days
CA15-3 testing is often repeated regularly during treatment and follow-up to track trends over time.
Test Preparation
- No fasting or special preparation is required.
- Inform your doctor about any ongoing liver disease, pregnancy, or benign breast condition, as these can mildly raise levels.
- Avoid testing immediately after surgery, infection, or inflammation, as these may affect results.
When to Consult a Doctor
You should consult a doctor if you experience:
- A new lump in the breast or armpit
- Changes in breast shape, size, or skin
- Persistent pain or nipple discharge
- Unexplained fatigue or weight loss
- High CA15-3 levels on repeat testing
Doctors may recommend additional tests like mammography, ultrasound, MRI, or biopsy to determine the underlying cause.
Important Word Explanations
- Tumor Marker: A substance produced by cancer cells or the body in response to cancer.
- Metastatic: Cancer that has spread from the original site to other parts of the body.
- Benign: Non-cancerous; not life-threatening.
- Fibrocystic Changes: Non-cancerous lumps or cysts in the breast.
- Cirrhosis: Scarring of the liver due to chronic disease.
- Endometriosis: Growth of uterine tissue outside the uterus.
- Remission: A period when cancer symptoms and signs reduce or disappear.
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