Challenges in the treatment of soft-tissue plasmacytoma: a retrospective analysis of 120 patients with extramedullary multiple myeloma

Despite the development of novel drugs and the widespread use of hematopoietic cell transplantation, the prognosis of patients (pts) with multiple myeloma and extramedullary involvement (soft-tissue plasmacytoma, STP) is rather unfavorable.

A retrospective analysis of 120 pts with STP treated between 2007 and 2022 was performed. The effects of demographic and clinical characteristics on treatment response, progression-free survival (PFS), and overall survival (OS) were evaluated.

The rate of serological response to first-line STP treatment (at least partial remission) was 67%, and the rate of imaging response was 59%. With a median follow-up of 84.2 months, the median PFS was 10.5 months (primary STP: 20.2 months; secondary STP: 5.8 months), and the median OS was 24.5 months (primary STP: 34.5 months; secondary STP: 12.4 months). Based on the multivariate regression analysis, secondary STP (HR_PFS 2.75; HR_OS 2.63) and organ involvement (HR_PFS 1.45; HR_OS 1.68) were found to be negative prognostic factors of both PFS and OS. In a prognostic model, pts with at least one of these factors had a significantly worse PFS (HR_PFS 3.31) and OS (HR_OS 3.45) than those with none risk factor.

In pts with STP, risk-adapted treatment strategies including immunotherapies and cell therapies are urgently required.