A radioimmunoconjugate comprised of the monoclonal antibody HuAFP31, directed against alpha fetoprotein, that is conjugated to the chelating agent tetra-azacyclododecanetetra-acetic acid (DOTA) and radiolabeled with the beta-emitting radioisotope Yttrium Y90. Yttrium Y 90 tacatuzumab tetraxetan binds to tumor cells expressing alpha fetoprotein, selectively delivering a cytotoxic dose of beta radiation.