Use of CA15-3 for screening breast cancer: An antibody-lectin sandwich assay for detecting glycosylation of CA15-3 in sera

Elevated serum CA15-3 assessed by enzyme-linked immunosorbent assay (ELISA) has been considered a diagnostic marker of breast cancer. However, accumulating data indicate that the current ELISA system for detecting CA15-3, which targets the peptide backbone of CA15-3, is not sufficiently sensitive to detect early or localized breast cancer. In the present study, we designed an antibody-lectin sandwich assay detecting glycosylation of CA15-3 in patients with breast cancer. Immobilized anti-CA15-3 monoclonal antibody captures CA15-3 in serum, and glycosylation of the CA15-3 is detected with Concanavalin A (ConA) lectin, which preferentially bind high-mannose N-glycans. ConA provided the best signal for detecting serum CA15-3 among 9 types of lectin, Since CA15-3 is a heavily glycosylated protein, detecting the glycosylation of CA15-3 should be a much more sensitive way to assess CA15-3 than the current ELISA method. Linear responses were obtained in the anti-CA15-3 antibody-ConA sandwich assay when sera were diluted up to 2000-fold. This dilution factor is comparable with that of the current ELISA system which allows 50- to 100-fold serum dilutions. The glycosylation level of CA15-3 was found to increase with increasing breast cancer stage in the sandwich assay. The assay system appeared to efficiently discriminate breast cancer stage I (sensitivity: 63%, specificity: 69%), IIA (sensitivity: 77%, specificity: 75%), IIB (sensitivity: 69%, specificity: 86%) and III (sensitivity: 80%, specificity: 65%) from benign breast disease. The antibody-lectin sandwich assay shows promise as a new prospect for the early detection of breast cancer.