CA 15-3 is a trans-membrane glycoprotein whose synthesis is encoded by the gene MUC1.

The main utility of this marker determination is monitoring and treatment of disease in breast cancer.

-CA 15-3 is useful for early detection of tumor recurrence in patients previously treated for breast carcinoma stages II and III without clinical signs of disease activity; elevated levels of CA 15-3 in a patient with breast cancer metastases indicate a high probability;

-Decreases in serum levels of CA 15-3 is an indicator of therapeutic response, while persistent elevated levels are associated with disease progression and inadequate response to therapy;

-Determining CA 15-3 and CEA combined may increase the sensitivity of detection of tumor recurrence; Serial determinations may be useful in early detection of bone metastases and liver.

Normal values: ​​<35 U / mL.

Determination of CA 15-3 is not recommended for screening, diagnosis and staging of breast cancer for the following reasons:

• localized breast tumors are rarely accompanied by heightened levels of CA 15-3;

• increases of  the marker can be registered in other clinical conditions:

     – Non-breast malignancies: pancreatic adenocarcinoma, lung, ovarian, liver;

     – Benign conditions: breast (mastitis, fibroadenoma), liver (hepatitis, cirrhosis).