The impact of extramedullary and paraskeletal plasmacytomas on treatment outcomes in multiple myeloma treated with teclistamab: U.S. Myeloma Immunotherapy Consortium real-world experience.

Teclistamab, a bispecific antibody targeting B-cell maturation antigen (BCMA), is effective in relapsed or refractory multiple myeloma (RRMM), but its impact on patients with soft tissue plasmacytomas is unclear. We studied 385 RRMM patients treated with teclistamab at 13 U.S. centers through September 2023, with follow-up to April 2024. Soft tissue plasmacytomas were classified as true extramedullary disease (EMD; not contiguous with bone) or paraskeletal plasmacytomas (PSK; contiguous with bone). Patients with the simultaneous presence of both were classified as true-EMD, reflecting its adverse prognosis. Of those, 109 (28%) had true EMD, 33 (9%) had PSK, and 243 (63%) had no soft tissue plasmacytoma (No-STP). Median follow-up was 9.9 months. Overall response rates were 38% in true-EMD, 54.1% in PSK, and 62.4% in No-STP (p < 0.001). Median progression-free survival (PFS) was 1.4 months in true-EMD, 6.51 months in PSK, and 8.95 months in No-STP (p < 0.0001). Median overall survival (OS) was 9.54 months for true EMD, 13.1 months for PSK, and not reached in No-STP (p = 0.00012). In multivariable analysis, true-EMD was independently associated with inferior PFS and OS, while PSK showed numerically lower outcomes. These findings highlight the need for tailored strategies in patients with soft tissue plasmacytomas, particularly those with true-EMD.