A radioimmunoconjugate composed of a humanized monoclonal antibody (MoAb) OTSA101 against FZD10 and labeled with yttrium Y 90, with potential antineoplastic activity. The MoAb moiety of yttrium Y 90-labeled anti-FZD10 monoclonal antibody OTSA101 binds to FZD10, thereby delivering a cytotoxic dose of beta radiation to FZD10 positive tumor cells. FZD10 (also called CD350), a member of the Frizzled family of G protein-coupled receptors that is involved in the Wnt/beta-catenin/TCF signaling pathway, is overexpressed in a variety of cancer cell types but undetectable in normal, healthy human tissues except the placenta.