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CA 15-3
Tumor marker used in monitoring breast cancer. Not a screening test — its role is tracking treatment response and recurrence.
Other names: Cancer antigen 15-3, carbohydrate antigen 15-3Section: Tumor markers
Updated: August 31, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortCA 15-3 is a protein that can rise in breast cancer. A common upper reference limit is about 30 U/mL. The test is not used to screen or diagnose on its own; its main value is following known disease — response to therapy and early signs of recurrence.
Reference ranges
Group
Reference range
Typical upper limit — typical range (international reference, not a national standard)
up to 30 U/mL
Limit quoted by the University of Rochester Medical Center encyclopedia (international reference, not a national standard). The report's own interval applies. Reference ranges vary between laboratories and assays — use the range printed on your own lab report.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
CA 15-3 is shed by breast cancer cells into the blood. Levels often track the course of metastatic disease: falling with effective treatment and rising with progression.
Levels can also rise in benign conditions — liver disease, benign breast disease, pregnancy — which is why a single elevated value never proves cancer.
When it is high
Breast cancer (known disease)Rising levels during follow-up can signal progression or recurrence; falling levels suggest response.
Benign breast and liver conditionsModerate elevations occur without cancer, especially with liver disease.
Other cancersOvarian, lung, and other cancers can also raise the marker.
When it is low
Expected findingMost healthy people — and many patients with early breast cancer — have low values.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Liver diseaseBenign breast diseasePregnancy
How to prepare
Blood from a vein; no special preparation.
When a retest makes sense
During cancer follow-up — on the oncologist's schedule. An isolated moderate elevation without a diagnosis is usually rechecked in 1–2 months.
Who usually reviews this result
A result outside the reference range is usually reviewed by: a gynecologist or breast specialist; an oncologist for known disease. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: CA 15-3Cancer antigen 15-3Carbohydrate antigen 15-3
Units
Measured in: U/mL
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
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