A monoclonal antibody (MoAb) directed against the MN protein with potential antineoplastic activity. Upon administration of BAY79-4620, this MoAb may stimulate the immune system to mount a cytotoxic T-lymphocyte (CTL) response and an antibody mediated cellular cytotoxicity (ADCC) against MN-expressing tumor cells. MN, a transmembrane glycoprotein, is expressed in some human carcinomas and appears to be involved in cancer cell proliferation and transformation.