Recombinant Anti-CEA x Anti-DTPA Bispecific Antibody (scDiabody-CH3) is a fusion protein of two scDiabodies connected together by a CH3 region. In single-chain Diabodies, an additional connecting linker is introduced between chains of the anti-CEA/anti-DTPA diabody. The scDiabody with two specificities is fused to each of the CH3 chains to extend half-life. This BsAb can be used in pretargeting system of PET, radioimaging or radiotherapy. It can mediate targeting of radioactivity to tumor cells. It is designed for the research of Breast cancer; Ovary cancer; Colon cancer; Lung cancer imaging and therapy.