Extramedullary disease (EMD) in multiple myeloma (MM) is associated with aggressive clinical behavior and poor prognosis, particularly when involving the lung parenchyma, which is an extremely rare manifestation. Bispecific antibodies targeting B-cell maturation antigen (BCMA), such as teclistamab, have recently demonstrated promising efficacy in heavily pretreated relapsed/refractory multiple myeloma (RRMM). However, evidence regarding their activity in patients with pulmonary extramedullary involvement remains limited. We report the case of a 76-year-old man with IgA-κ RRMM who developed multiple extramedullary lesions, including pulmonary nodules, after progression on several lines of therapy. Following initiation of teclistamab, the patient experienced grade 1 cytokine release syndrome that resolved rapidly after tocilizumab administration. An abdominal wall mass transiently enlarged early after treatment initiation, raising suspicion of pseudoprogression. Subsequently, all extramedullary lesions, including the pulmonary nodules, showed marked regression, with complete radiologic resolution observed by day 80. At 4.5 months after treatment initiation, both positron emission tomography–computed tomography and bone marrow multiparameter flow cytometry demonstrated minimal residual disease negativity. The patient has continued teclistamab therapy with sustained disease control. This case illustrates that teclistamab may provide meaningful clinical benefit even in RRMM with pulmonary extramedullary involvement, a condition typically associated with extremely poor outcomes. Our findings also suggest that transient lesion enlargement early after therapy may represent pseudoprogression and should be interpreted cautiously in patients receiving bispecific antibody therapy.
Takakuwa et al. (2026) studied this question.