1) The breast cancer antigen was detected by the immunodiffusion technique with rabbit anti-breast cancer serum which was absorbed with pooled normal human plasma and extracts of non-m alignant breast glands. All extracts of eighteen breast cancer tissues and extracts of normal liver, spleen and kidney were reacted with the antiserum. No precipitation band was found between ex tracts of non-malignant breast glands and digestive tracts, and the antiserum.
2) The antigenic substance was purified from pooled breast cancer extracts by ammonium sulfate fractionation, Sephadex G-200 gel filtration, column chromatography with DEAE-Sephadex A-50 and preparative polyacrylamide gel electrophoresis at pH 9.5. Single protein band was obtained for the isolated substance in polyacrylamide gel electrophoresis.
3) The antigenic substance was glycoprotein that was stained by PAS reagent, and was migrated on immunoelectrophoresis as a single line in the α-region. The molecular weight was estimated to be 5 6 × 106 by Sephadex G-200 gel filtration. The antigenic activity was destroyed at 80°C for five minutes.
4) The immunochemical characteristics of the breast tumor-associated antigen were different from common tumor-associated antigens previously reported such as the carcinoembryonic antigen (CEA) and the α-fetoprotein. Some association between the breast cancer antigen and the α2H-globulin was discussed.