A humanized monoclonal antibody directed against the activator of g-proteins signaling (AGS) cell surface protein AGS-8 with potential antineoplastic activity. Anti-AGS-8 monoclonal antibody AGS-8M4 selectively binds to AGS-8, triggering complement-dependent cell lysis and antibody-dependent cell-mediated cytotoxicity in tumor cells expressing AGS-8. While normally expressed at low levels in the heart in response to ischemia, AGS-8 has been found to be expressed in more than 70% of ovarian neoplasms.