Long-term clinical outcomes in a cohort of patients with solitary plasmacytoma treated in the modern era

Background The risk of recurrence of solitary plasmacytoma (SP)/progression to MM is well established, but patient, imaging and treatment factors influencing risk of progression require further evaluation. Methods This is a retrospective analysis of 66 SP patients (23 UK, 43 Brazil) diagnosed 1989–2016. Patient baseline characteristics were recorded. The incidence of progression to MM was calculated, including biochemical and imaging findings and the treatment modality received. Survival estimates were determined by Kaplan-Meier analyses. Results With a median follow-up of 53.6 months the 5 year overall survival (OS) was 90.7% (95%CI 79–96%). The median progression free survival (PFS) from diagnosis was 61 months. Cumulative incidence of progression to MM was 49.9% at 5 years (95% CI 35.6–62.6%) and was significantly higher with bone plasmacytoma (47.2%, 95%CI 31.9–61.1%), than an extramedullary location (8.3%, 95%CI 0.4–32.3%, Gray test p = 0.0095)). The majority of patients with solitary bony plasmacytoma (SBP) received radiotherapy (RT) (51/53, 96.2%) whereas most extramedullary cases were treated with surgical resection (7/13, 53.8%). A small proportion of SBP patients received additional upfront chemotherapy, with 5/6 in remission after a median follow-up (FU) of 10 years. The diagnostic yield of surveillance functional FU imaging without other indications of relapse/progression was low. The positive predictive value of functional FU imaging was high but with a low negative predictive value, especially in cases of suspected relapse/progression. Conclusion Our data suggests functional imaging should be used if clinical suspicion of relapse/progression, rather than a routine surveillance tool, and upfront adjuvant chemotherapy is worthy of prospective evaluation.