CAR-T cell therapy for patients with extramedullary multiple myeloma：Opportunities and challenges

Multiple myeloma (MM) is a hematological malignancy characterized by abnormal proliferation of clonal plasma cells, which is usually confined to the bone marrow (BM). But some malignant plasma cells grow independently of the BM, called extramedullary disease (EMD). With the clinical application of proteasome inhibitors, immunomodulators, monoclonal antibodies, and hematopoietic stem cell transplantation, the overall survival of MM patients has been significantly improved, but the survival of patients with EMD is still worse than that of non-EMD patients. There are currently no specific treatment options for EMD. chimeric antigen receptor T (CAR-T) cell therapy has brought a new era of immunotherapy. The application of CAR-T has significantly benefited many MM patients, and CAR-T may be a new hope for patients with EMD in the future. This review retrospectively summarizes the mechanism and prognosis of EMD, focusing on the application and potential of CAR-T in the treatment of EMD. It is hoped that this review can provide ideas for the treatment of EMD with CAR-T in the future.