New breast cancer marker BF-09 is overexpressed in tumor extracts and secreted in serum

Background: CA 15-3 and CA 27-29 are widely used serum biomarkers for breast cancer with limited utility due to low sensitivity in early-stage disease. This study details the discovery of BF-09, a new breast cancer marker with potential for wider application. Method: Antibodies were screened against tumor biopsy extracts (n = 115) relative to non-cancer (n = 190) specimens using an immunoscreening array. Western blot was done to determine the molecular weight of the antibody target and test secretion in cell culture medium. A sandwich ELISA was developed and tested on mouse xenograft serum to confirm in vivo secretion. A preliminary set of cancer (n = 14) and non-cancer (n = 13) human serum samples was similarly tested to confirm the biomarker could be measured in human blood. HuProt Human Protein Array was used for target protein identification. Results: BF-09 antibody was selected for further study because its protein target was elevated in both early and late-stage cancer extracts (p < 0.05). On Western blot, BF-09 antibody reacted against a protein band of around 15 kDa. ELISA results confirmed that the biomarker was secreted in both mouse and human serum in quantifiable amounts. BF-09 protein had higher median concentration in serum of cancer patients (p < 0.0001) compared to non-cancer patients. Phage display and HuProt array revealed the protein target as SAGA-associated factor 29. Conclusion: Due to its elevated presence in early-stage tumor tissue and its measurable secretion into serum, BF-09 is a promising breast cancer marker for further study.