Labetuzumab is a humanized monoclonal antibody that targets the carcinoembryonic antigen (CEA or CEACAM5), a glycoprotein highly expressed on the surface of many cancer cells, particularly those of colorectal and gastrointestinal origin. Its primary therapeutic strategy is to deliver a cytotoxic payload (e.g., a radioisotope or drug conjugate) directly to CEA-positive tumors. While investigated as a naked antibody, its most significant development has been as a component of antibody-drug conjugates (ADCs) or radioimmunoconjugates for targeted cancer therapy. Despite showing promise in early studies, its clinical development for metastatic colorectal cancer has been challenging.