Abstract
Serum from patients with systemic breast cancer was found to contain elevated levels of polymorphic epithelial mucin (PEM) as detected using an immunoradiometric assay employing the monoclonal antibody NCRC-11. PEM was partially purified from pooled sera from these patients and the complex, polymorphic, high-molecular-mass (greater than 400 kDa) mucin was identified by sodium dodecylsulphate/polyacrylamide gel electrophoresis, Western blotting and immunostaining with the NCRC-11 antibody. Serial serum samples from 16 patients with metastatic breast cancer were assayed for circulating PEM defined by the monoclonal antibody NCRC-11. The clinical course of disease in these patients was assessed independently as progressive, static or responsive. Increasing NCRC-11 antigen levels correlated with disease progression in 6/7 patients, and decreasing antigen levels correlated with an objective response to treatment in 5/6 patients. Measurement of NCRC-11-defined PEM antigen in patients undergoing therapy for metastatic breast cancer showed an overall accuracy of 75%.