Relapse with plasmacytoma after upfront autologous stem cell transplantation in multiple myeloma

Plasmacytoma has been reported to be associated with a poor prognosis in patients with multiple myeloma (MM). In this study, we evaluated the incidence of relapse with plasmacytoma and survival outcomes after upfront autologous stem cell transplantation (ASCT). This study retrospectively analyzed the data of 303 patients with MM who underwent upfront ASCT between April 2000 and April 2018 at eight institutes in the Republic of Korea. In total, 52 patients (17.1%) had plasmacytoma at MM relapse after upfront ASCT, of whom, 27 had paramedullary plasmacytoma (PMD) and 25 had extramedullary plasmacytoma (EMD). Patients with initial plasmacytoma were more likely to have plasmacytoma at MM relapse than those without initial plasmacytoma (37.1% vs. 11.2%). Over a median follow-up of 66.0 months, patients with plasmacytoma at relapse had significantly inferior overall survival (OS) than those without plasmacytoma (43.9 vs. 100.7 months, P < 0.001), but the OS did not significantly differ between patients with EMD and those with PMD (42.2 vs. 56.6 months, P = 0.464). After MM relapse, all patients received salvage therapy, and progression-free survival after relapse was significantly shorter in patients with plasmacytoma than in those without (6.4 vs. 12.4 months, P = 0.007). This study showed that plasmacytoma frequently developed at MM relapse after upfront ASCT in patients with plasmacytoma at the time of diagnosis. Plasmacytoma at relapse was significantly associated with a poor prognosis.