Comparison of outcomes after autologous stem cell transplantation between myeloma patients with skeletal and soft tissue plasmacytoma

We aimed to compare the characteristics of skeletal and soft tissue plasmacytomas and to analyze clinical outcomes and prognostic factors of autologous stem cell transplantation (ASCT) in multiple myeloma (MM) patients with plasmacytoma. We retrospectively reviewed data from 93 myeloma patients with detectable extramedullary (EM) plasmacytoma at diagnosis or during the course of the disease, who underwent ASCT. Soft tissue plasmacytoma occurred more frequently in male patients and had higher levels of serum 2-microglobulin and lactate dehydrogenase and high frequency of advanced disease according to International Staging System compared to the skeletal plasmacytoma group. Both soft tissue and skeletal plasmacytoma groups showed similar plasmacytoma relapse patterns after ASCT and relapsed with EM plasmacytoma slightly more frequently in the bone compared to soft tissue sites. Compared to patients with skeletal plasmacytoma, patients with soft tissue plasmacytoma had worse median progression-free survival (PFS) (12 vs. 28months) (P=0.001) and overall survival (OS) (37 vs. 67months) (P=0.037) after ASCT. In a multivariate analysis, soft tissue plasmacytoma was an only independent poor prognostic factor for both PFS (HR, 2.398; 95% CI, 1.304-4.410) and OS (HR, 2.811; 95% CI, 1.107-7.135) after ASCT. These results demonstrate that, even though ASCT achieved a strong response in myeloma patients with soft tissue plasmacytoma, the presence of EM disease still contributed to a poor prognosis after ASCT compared to skeletal plasmacytoma, and these poor outcomes were not overcome by ASCT.