A Clinical Model of Progression to Multiple Myeloma in Solitary Plasmacytoma

Introduction: Solitary plasmacytoma is a malignant collection of plasma cells (PC) in the soft tissue (EP) or skeleton (BP) without multiple myeloma (MM). Treatment is based on excision and/or radiation therapy. A proportion of patients with EP/BP progress to MM. In this study we describe the baseline characteristics/clinical outcomes and create a clinical model of progression in a large cohort of 98 plasmacytoma patients diagnosed between 1986 and 2015. Methods: We retrospectively searched our PC database from 1986-2015. 218 patients were identified, of whom 120 were excluded due to incorrect diagnosis (n=40)/lack of baseline data (n=78)/duplicate patient (n=2). Summary statistics were given for categorical and continuous variables. Chi-squared and Fisher9s exact tests were used to examine the associations between categorical variables and Wilcoxon9s rank sum test was used for continuous variables. The primary outcomes were time to myeloma (TTM:time from diagnosis to myeloma progression), progression free survival (PFS:time from diagnosis to myeloma progression or death) and overall survival (OS:time from diagnosis to death of any cause). Kaplan-Meier curves were plotted for PFS/OS/TTM. Univariate cox proportional hazard models were used to determine the effects of potential risk factors (RF) on TTM, PFS and OS. Multi-covariable Cox proportional hazard models were used to identify RF on time to myeloma. A multi-covariable Cox regression model was fitted using backwards variable selection with a p-value of ≤ 0.05 as limit for inclusion. All tests are two-sided. All analyses were conducted using SAS 9.4 (SAS, Cary, NC) and S-Plus 8.0 (TIBCO Software Inc., Palo Alto, CA) software. Results: Figure 1a shows baseline patient/treatment characteristics. Most patients (n=88/98; 90%) had advanced imaging (MRI, PETCT, CT scan) and bone marrow biopsy at diagnosis (n=97/98; 99%). The median follow-up time was 7.64 years (range 0.2-23.5) among the 64 alive patients. There were 42 myeloma progressions among the 98 patients. BP (n=34/67; 50%) progressed at a significantly higher rate than EP (n=8/31; 25%; p=0.02) (Figure 1b). On univariate analysis baseline bone plasmacytoma, lower hemoglobin, immunoparesis, presence of blood paraprotein and increased light chains in blood were associated with unfavorable TTM outcome (p Conclusion: BP and EP are precursors of MM. At a median follow up of 7.64 years, 26% of EP and 51% of BP patients progressed to MM. These rates are similar to those reported for low and intermediate risk smoldering myeloma, emphasizing the need for continued follow up and prevention strategies (i.e., study NCT02516423 of systemic treatment with ixazomib, lenalidomide, dexamethasone, zoledronic acid). Clinical models such as the one presented here may guide clinicians in optimal follow up or inclusion in clinical trials for prevention of progression to MM. Disclosures Manasanch: takeda: Consultancy; sanofi: Research Funding; adaptive biotechnologies: Consultancy; merck: Research Funding; celgene: Consultancy; quest diagnostics: Research Funding. Lee: Takeda: Consultancy; Celgene: Consultancy; Pimera Inc: Consultancy; Adaptive: Membership on an entity9s Board of Directors or advisory committees; Eutropics Pharmaceuticals: Research Funding; Daiichi Sankyo: Research Funding. Thomas: Celgene: Research Funding; Bristol Myers Squibb: Research Funding. Patel: Juno: Consultancy; Celgene: Consultancy; Pfizer: Membership on an entity9s Board of Directors or advisory committees, Research Funding. Orlowski: BioTheryX: Consultancy, Membership on an entity9s Board of Directors or advisory committees.