Dramatic Response to Elranatamab in a Patient with Large Plasmacytomas

To the Editor, Despite significant advances, including proteasome inhibitors, immunomodulatory drugs, and monoclonal antibodies, treatment outcomes remain unsatisfactory, particularly in patients with relapsed/refractory multiple myeloma (RRMM) presenting with extramedullary (EMD) disease.[1,2] Elranatamab is a bispecific antibody developed for the treatment of MM. [2-4] It has been approved as monotherapy for RRMM based on the phase II MagnetisMM-3 study.[3] A 71-year-old female patient was diagnosed with MM and plasmacytoma in September 2015 at the age of 62. Her R-ISS stage was II, and no myeloma-specific molecular abnormalities were detected.She received 4 cycles of bortezomib, cyclophosphamide, and dexamethasone along with radiotherapy, followed by autologous stem cell transplantation (ASCT) with 200 mg melphalan conditioning.At the third month post-transplant, a complete medullary and partial EMD response was achieved.She subsequently received six cycles of bortezomib, lenalidomide, and dexamethasone, followed by lenalidomide maintenance therapy.In May 2023, positron emission tomography/computed tomography (PET-CT) revealed a recurrent expansile mass in the sacrum.Treatment was switched to carfilzomib, lenalidomide, and dexamethasone.After six cycles, a partial response was achieved; however, at the 16th cycle, disease progression was detected with a new 6-cm mass in the sacrum.The lesion was treated with involved-field radiation therapy.Subsequently, daratumumab, pomalidomide, and dexamethasone were initiated.After two cycles, serum protein electrophoresis (SPEP) showed a significant increase in M-protein (1.1 g/dl to 2.9 g/dL), and the serum free-lightchain (FLC) ratio was 36 (with a serum free lambda level 132 mg/dL and kappa level 3,67 mg/dL).PET/CT demonstrated multiple lesions in the axial and appendicular skeleton, in both scapulae, and the largest one-measuring 5.84.5cm-waslocated at the anterior end of the second rib, extending toward the pleura and lung parenchyma, with an associated soft-tissue component.One of which was visibly located in the oral cavity (Figure 1A).As biochemical progression was evident, a bone marrow biopsy was not performed; however, a tru-cut biopsy taken from the oral lesion was consistent with lambda-positive plasma cell infiltration.As fifth-line therapy, elranatamab monotherapy was started.The patient developed grade 1 cytokine release syndrome, grade 2 thrombocytopenia, grade 3 neutropenia during treatment u