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

## TL;DR

This study shows that patients with extramedullary plasmacytomas had worse outcomes when treated with teclistamab for multiple myeloma compared to those without soft tissue plasmacytomas.

## Contribution

The study provides real-world evidence on how soft tissue plasmacytoma subtypes affect treatment outcomes with teclistamab in multiple myeloma patients.

## Key findings

- Patients with true extramedullary disease had significantly lower overall response rates and shorter progression-free survival compared to others.
- Median overall survival was notably shorter in patients with true extramedullary disease versus those without soft tissue plasmacytomas.
- True extramedullary disease was independently associated with worse progression-free and overall survival in multivariable analysis.

## Abstract

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.