Lilotomab is a murine monoclonal antibody that specifically targets the CD37 antigen, a tetraspanin protein highly expressed on the surface of B cells and certain B-cell malignancies. It is not used as a standalone therapeutic but functions as a pretargeting agent in a novel radioimmunotherapy approach. In this strategy, unlabeled lilotomab is administered first to bind to CD37-positive tumor cells. Subsequently, a small, fast-clearing radionuclide chelator (e.g., 177Lu-DOTA-betan) is given, which rapidly binds to the pre-localized antibody on the tumor. This two-step method aims to deliver a highly cytotoxic radiation dose specifically to tumor cells while minimizing exposure to healthy tissues. It has been investigated in clinical trials for the treatment of relapsed or refractory non-Hodgkin lymphoma (NHL), particularly follicular lymphoma.