Serum paraprotein persistence and size determine outcome in a cohort of patients with a modern definition of plasmacytoma with up to 19 years of follow up

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Solitary plasmacytoma (SP) is a rare plasma cell disorder (<5% of all plasma cell dyscrasias) that consists of solitary bone plasmacytoma (SBP) and solitary extramedullary plasmacytoma (SEP). Local control with radiation therapy (RT) remains the standard of care. About half of all patients progress to multiple myeloma (MM) within 3–5 years after diagnosis 1 . Several factors identify SP patients that are at high risk of progression to MM (location, bone marrow (BM) involvement, serum free light chain values (sFLC), paraprotein persistence, and size). Identification of patients at high risk of progression to MM is an important step to design prevention strategies. In smoldering myeloma, randomized studies have shown increased progression-free survival (PFS) and overall survival (OS) after systemic treatment 2 , 3 and immunotherapeutic strategies in this space are promising 4 , 5 . Due to a limited number of cases, prospective evaluation of prevention strategies in SP has remained elusive.