The CA15.3 (Cancer Antigen 15-3) assay uses monoclonal antibodies to detect two antigenic sites associated with breast carcinoma cells. It is used primarily as a marker for cancer of the breast, but may also be elevated in cancers of the stomach, liver, pancreas, lung and ovary. As with other tumour markers, CA15.3 is most useful for serial monitoring.

Non-malignant elevations may be seen in hepatitis and cirrhosis.

CA15.3 is an MEIA assay performed on the Abbott AxSYM. Samples can be serum (preferred) or plasma.

Reference Range = <28 kU/L​​

Borderline levels = 28-60 kU/L

Interferences: HAMA.