Rethinking mechanisms of neurotoxicity with BCMA directed therapy.

B-cell maturation antigen (BCMA) has become a key target for antibody-drug conjugates, bispecific antibodies, chimeric antigen receptor T-cell therapies, and other immunotherapies in multiple myeloma. Some of these agents such as belantamab mafodotin and idecabtagene vicleucel have already received regulatory approval in the United States. Although BCMA has generally been considered to be expressed almost exclusively in plasma cells with a low likelihood of on-target off-tumor toxicity, there has been a range of unusual neurotoxicity observed across the spectrum of BCMA immunotherapies. In certain cases, these unusual neurotoxicity presentations have led to patient death or withdrawal of agents from further development. Our review summarizes the literature in this field and highlights the possibility of on-target toxicities due to neural expression of BCMA. We draw attention to the need for further investigation of these toxicities. This risk becomes increasingly important as BCMA targeted therapies are brought to earlier lines of treatment.