A polypeptide, which is expressed on the cell surface as a membrane-bound protein, is glycolyzed at one or more points (i.e., membrane glycoprotein) and has an amino acid sequence that corresponds partially or completely to that of the integrin binding protein p80 (accession #AJ131720) or REV1 (accession #AF206019.) The membrane glycoprotein, is expressed by neoplastic cells and not by non-neoplastic cells as an antigen, specifically binds the human monoclonal antibody PM-2 (DSM number: DSM ACC2600) and is, in addition, N-glycosidically and O-glucosidically linked. A related method is provided for the isolation or production of the antigen and for the use of the latter for producing a medicament for immunization. The isolated antigen can also be used to identify medicaments with an apoptotic cell-proliferation inhibiting action. The membrane glycoprotein can also be used as a tumor marker.