CEACAM5 and neoplasm: For example, immunoPET using 89Zr‐ labeled BsAb, which binds CD3 and carcinoembryonic antigen (CEA) to activate T cells in patients with gastrointestinal cancer, was studied in a clinical trial (Figure 6A–C).[64] The CD3/CEA‐specific BsAb accumulated in tumor lesions as well as lymphoid organs, offering insights into the diversity of antigen expression.