Abstract
Glycoproteins were isolated from membrane preparations of human breast cancer using lithium di‐iodosalicylate followed by phenol partition as described for the isolation of CEA from colonic carcinoma. The glycoprotein isolated from breast cancer‐(BCGP) differed from colonic CEA in extraction yield, antigenicity, molecular weight on SDS acrylamide gel electrophoresis and on immunoelectrophoresis. Rabbit anti‐serum raised against BCGP and absorbed with red blood cells and normal breast tissue showed a reaction of identity on Ouchterlony immunodiffusion between BCGP and CEA. However, antiserum to CEA absorbed with red blood cells and normal colonic mucosa showed cross‐reaction of BCGP with CEA. The anti‐BCGP activity in anti‐CEA could be removed by absorption with BCGP, leaving activity directed only against CEA. Therefore, BCGP appears to be a CEA‐like antigen that shares antigenic determinants with CEA and may be responsible for the elevated radioimmunoassays for CEA in breast cancer patients. Whether there is a breast‐cancer‐specific antigen associated with the cell membrane remains to be demonstrated.