Cancer Antigen (CA) 15-3

Cancer Antigen (CA) 15-3, also known as cancer antigen 15-3 or carbohydrate antigen 15-3, is used to monitor therapeutic response and to surveil for recurrence in breast carcinoma, particularly when a patient’s baseline CA 15-3 is elevated. When interpreted with clinical examination and imaging findings, results may aid in differentiating benign from malignant breast conditions. Concentrations generally reflect tumor burden and can be trended over time to inform management.

CA 15-3 is a high–molecular-weight mucinous glycoprotein produced by normal mammary epithelium and overexpressed in many breast carcinomas. Serum concentrations are elevated in approximately 10% of early-stage breast cancer and in about 70% of metastatic disease. The assay is not sufficiently sensitive or specific for diagnosing early breast cancer, and results require correlation with clinical assessment and other diagnostic procedures. Elevated CA 15-3 is not unique to breast malignancy. Increased levels may occur with other cancers (eg, colorectal, lung, ovarian, cervical, endometrial), with benign breast disease, in chronic liver disorders such as hepatitis and cirrhosis, and during pregnancy.