Understanding CA 15-3
The CA 15-3 test measures Cancer Antigen 15-3, a protein produced by various cells, including those in breast tissue. This protein enters the bloodstream, where its levels are detected through a blood test. It is considered a tumor marker because its concentrations can increase with certain cancers.
A normal CA 15-3 level is less than 30 units per milliliter (U/mL). Labs may have slightly different reference ranges. An elevated level, particularly one over 100 U/mL, requires further medical evaluation to understand its underlying cause.
Causes of Elevated CA 15-3
An elevated CA 15-3 level can stem from various conditions, both cancerous and non-cancerous. It is most recognized in advanced or metastatic breast cancer. Higher levels often correlate with a larger tumor burden or spread to distant sites like the liver or bones. About 76% of individuals with metastatic breast cancer show elevated levels, with highest concentrations often seen when cancer has spread to the liver or bones.
Other cancers can also lead to increased CA 15-3 levels. These include:
Lung cancer
Ovarian cancer
Colon cancer
Liver cancer
Pancreatic cancer
Prostate cancer
Endometrial cancer
Bladder cancer
While these can cause elevations, breast cancer is where CA 15-3 is most frequently elevated and used as a marker.
A high CA 15-3 level does not automatically indicate cancer. Non-cancerous conditions can also cause elevations, such as liver diseases like hepatitis and cirrhosis. Inflammatory conditions, including sarcoidosis, tuberculosis, or systemic lupus erythematosus, can also elevate levels.
Benign breast conditions, like fibroadenomas or mastitis, can cause mild to moderate increases in CA 15-3. Other non-cancerous causes include pelvic inflammatory disease and endometriosis. Physiological states like pregnancy and lactation can temporarily elevate CA 15-3 levels. In non-cancerous conditions, CA 15-3 levels tend to remain stable, unlike the progressive increases seen with active cancer.
Role in Cancer Management
CA 15-3 is used to monitor the progression of certain cancers, particularly metastatic breast cancer, and to assess treatment effectiveness. A decrease in CA 15-3 levels indicates tumor response. Conversely, stable or increasing levels, despite therapy, suggest treatment is ineffective or cancer is progressing.
It also helps detect cancer recurrence after initial treatment. A rising trend in CA 15-3 levels over time, especially after a period of stable or decreasing levels, can signal recurrence. Very high CA 15-3 levels can indicate a more advanced stage or larger tumor burden.
CA 15-3 is not a screening tool. It is not used for screening or to definitively diagnose cancer. It lacks sensitivity for early detection, as levels may not be elevated in early breast cancer. About 20% to 30% of people with advanced breast cancer may not have tumors that release detectable amounts of CA 15-3.
Its lack of specificity also limits its use as a standalone diagnostic tool, as benign conditions can cause elevations. CA 15-3 is always interpreted with other clinical information, physical examinations, and imaging studies.
Interpreting Your Results and Next Steps
Receiving a CA 15-3 level over 100 U/mL can be concerning, but discuss results with a healthcare provider. A single elevated reading is rarely conclusive alone and requires further investigation. Your doctor will consider your medical history, symptoms, and other factors to interpret the result.
A comprehensive evaluation often involves additional diagnostic tests to find the reason. These may include imaging studies like mammograms, ultrasounds, magnetic resonance imaging (MRI), or computed tomography (CT) scans to visualize organs. Other blood tests may assess organ function or look for additional markers. In some cases, a biopsy may be recommended.
The interpretation of your CA 15-3 level is individualized, as its meaning varies by health profile. Based on these findings, your doctor will determine next steps. This could range from monitoring CA 15-3 levels to initiating specific treatment if a condition is diagnosed.