title: MUC1 gene-derived glycoprotein assays for monitoring breast cancer (CA 15-3, CA 27.29, BR): are they measuring the same antigen?
abstract: BACKGROUND
  There are 2 general types of assays measuring MUC1 gene-derived glycoprotein: assays for cancer antigen (CA) 15-3, which are sandwich assays, and assays for CA 27.29, which are competitive assays. These 2 types of assays measure slightly different parts of this tandem-repeat molecule. Across-method assay differences hinder the exchange of patient test values among integrated health care networks and among countries.
  
  
  OBJECTIVE
  This report evaluates the method differences among these assays to determine if the differences between these assays are mainly related to variations in calibration or differences in analyte specificity.
  
  
  METHODS
  Data from 22 College of American Pathologists survey challenges were analyzed to compare 10 commercial assay methods for these 2 related analytes. In addition, data from 58 patient samples were analyzed to compare 3 of these assays.
  
  
  RESULTS
  The linear correlation coefficients comparing the within-method medians of these proficiency test distributions were very high (>0.99) for all of the methods; however, the regression slopes varied from 0.836 to 1.095. The regression slopes for the patient specimens varied similarly, but the correlation coefficients were lower.
  
  
  CONCLUSIONS
  This study indicates that many of the test value differences for these measurements are due to differences in assay calibration rather than differences in the specificity of the assay measurement systems. Survey test data potentially could be used to help harmonize these assay differences.
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic and Foundation, Rochester, Minn 55905, USA. klee.george@mayo.edu
authors.forename: George G
authors.initials: GG
authors.lastname: Klee
authors.forename: William E
authors.initials: WE
authors.lastname: Schreiber
mesh_terms: D000918:Antibody Specificity; D015295:Antigens, Tumor-Associated, Carbohydrate / Q000276:immunology*; D001667:Binding, Competitive; D014408:Biomarkers, Tumor / Q000276:immunology; D001943:Breast Neoplasms / Q000473:pathology*; D002138:Calibration / Q000592:standards; D019411:Clinical Laboratory Techniques / Q000592:standards; D003625:Data Collection / Q000379:methods; D019084:Fluorescent Antibody Technique, Indirect / Q000592:standards; D006023:Glycoproteins / Q000276:immunology; D006801:Humans; D018396:Mucin-1 / Q000276:immunology*; D010338:Pathology, Clinical / Q000592:standards; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015295:Antigens, Tumor-Associated, Carbohydrate; D014408:Biomarkers, Tumor; C090797:CA 27-29 antigen; D006023:Glycoproteins; D018396:Mucin-1