Recombinant Anti-CEA x Anti-DTPA Bispecific Antibody (Tandem Fab) is designed to be expressed as three chains derived from the variable domains of anti-CEA and anti-DTPA parental antibodies. It contains a His-tag for affinity purification. And the two Fd regions are connected by a flexible linker. 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.