Solitary plasmacytoma: should new approaches in diagnosis and treatment be adopted?

Abstract

Background: Radiotherapy (RT) is the gold standard for solitary plasmacytomas (SP) with great local control. The influence of radiotherapy as well as factors on multiple myeloma (MM) progression is unknown.

Materials and methods: We present a retrospective study of 27 patients with SP (bone-SBP- and extramedullary-SEP-), treated since 1995 to 2021. We aim to analyze prognostic factors affecting local control and progression to MM in patients treated with radiotherapy (RT).

Results: Mean age was 57.3 years. 22 were SBP and 5 SEP. 13 patients were treated with definitive RT, and 14 with a combination of RT and systemic treatment and/or surgery. Local control was observed in 91.5% of cases. 28% experienced progression to MM. With a median follow up of 61.4 months [39.5, 121.6], 5-years MM-free-survival was 81 ± 8%; no individuals progressed further 50 months since diagnosis. Large tumor bulk (> 5 cm) and type (SBP 36% vs. SEP 0%) were associated with progression. Progression was not affected by doses greater than 46 Gy and/or surgery. An immunophenotype different from IgG kappa was predictive of less progression (p = 0.031) in Cox regression analysis adjusted for age, RT dose and tumor bulk > 5 cm. Patients with positron emission tomography-computed tomography (PET-CT) staging showed less MM progression, without statistical differences.

Conclusion: RT achieves more than 90% of local control. The immunophenotype IgG kappa showed more risk of progression to MM. Initial staging with PET-CT seems to lead to a better identification of SP. The inclusion of bad prognosis patients in clinical trials would determine the role of adjuvant chemoimmunotherapy in SP treatment.