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Carbohydrate antigen 15-3 (CA15-3) is a hydrolyzed soluble form of mucin 1 (or MUC1). It was initially found that CA15-3 is a tumor antigen which can be recognized by both monoclonal antibodies DF3 and 115D8, among which DF3 recognizes the MUC1 core protein and 115D8 recognizes part of the glycan chain of MUC1. MUC1 is a highly glycosylated membrane-bound protein expressed on the top surface of epithelial cells in gastrointestinal tract, esophagus and other tissues. MUC1 is a member of the mucin family, with a molecular weight of about 400-450 kDa and is composed of α and β subunits. The N-terminal α subunit is cell-adhesive and can act as an adhesion protein or an anti-adhesion protein to provide a protective mucus barrier for epithelial cells to prevent from being attacked by bacteria and enzymes. The C-terminal β subunit of MUC1 can participate in the regulation of ERK, SRC and NF-kappa-B pathway cell signal transduction through phosphorylation and protein interaction. In activated T cells, it can also affect the Ras/MAPK pathway and promote tumor development.

Carbohydrate Antigen 15-3 (CA15-3) Reference Range

CA15-3 has been used as a biomarker for breast cancer since the 1980s. CA15-3 is located on the tumor cell membrane. When cell carcinogenesis occurs, glycosyltransferases are activated, leading to abnormal glycosylation on the cell surface. Meanwhile, the overexpression of MUC1 on the cell surface leads to its release into the bloodstream, resulting in an increase in serum CA15-3 levels. Research has revealed that CA15-3 levels are elevated in 30-50% of breast cancer patients, and the combined dynamic monitoring of CA15-3 and CEA (carcinoembryonic antigen) can be used to monitor the recurrence and metastasis of breast cancer.

Table 1. Reference range of CA15-3 in different detection systems

Detection System	RocheTM	Beckman CoulterTM	SiemensTM	AbbottTM
Reference Range (U/mL)	≤24	≤15	≤19	≤20

Note: Since there is no recognized traceability system for CA15-3, there are differences in test results between various systems.

References

[1] Xiulian Li, Yan Xu, Lijuan Zhang. Serum CA153 as biomarker for cancer and noncancer diseases[J]. Prog Mol Biol Transl Sci,2019,162: 265-276.