Synergistic effects of elranatamab and Juzentaihoto, Japanese traditional herbal medicine, in triple-class-exposed relapsed/refractory multiple myeloma with extramedullary disease: a case report.

Relapsed/refractory multiple myeloma (RRMM) with extramedullary disease (EMD) is associated with poor prognosis and limited response to standard therapies. Elranatamab, a bispecific antibody targeting BCMA and CD3, has demonstrated clinical activity in triple-class-exposed (TCE) RRMM but remains less effective in patients with EMD. We report a case of a 67-year-old woman with TCE RRMM and aggressive EMD that progressed after two cycles of elranatamab. Following the addition of Juzentaihoto (JTT), a traditional Japanese herbal medicine, rapid symptom improvement, tumor regression, and disappearance of M-protein on immunofixation were observed. Moreover, after JTT initiation, lymphocyte and CD4-CD8bright cell counts increased rapidly and robustly, suggesting that JTT may enhance the elranatamab-induced antitumor immune response via these cells. To our knowledge, this is the first in vivo report indicating that JTT increases CD4-CD8bright lymphocyte counts in humans. JTT may enhance the efficacy of T cell-redirecting immunotherapies in RRMM by promoting cytotoxic T cell expansion. These findings warrant further investigation into the use of JTT as an adjunct to improve outcomes in patients with EMD.