Background
Large retrospective multicenter study (Rare Cancer Network) of 258 patients with bone (n=206) or extramedullary (n=52) solitary plasmacytoma treated across multiple European and North American centers. Most (n=214) received RT alone; 34 received chemo+RT; 8 had surgery alone. Median RT dose 40 Gy. Median follow-up 56 months.
Interventions and follow up
Arm A: Radiotherapy alone (n=214)
Arm B: Chemo + RT (n=34) or surgery alone (n=8); retrospective, no randomizatio
Primary endpoint: Overall survival, disease-free survival, local control, progression to MM
mFollow up: 56 months (median)
Arm B: Chemo + RT (n=34) or surgery alone (n=8); retrospective, no randomizatio
Primary endpoint: Overall survival, disease-free survival, local control, progression to MM
mFollow up: 56 months (median)
Results
5-Year OS: 74%
5-Year DFS: 50%
5-Year Local Control: 86%
5-Year Progression to MM: 45%; bone SP 51% vs. extramedullary SP 25%
Dose-response: No dose-response relationship for RT doses >30 Gy, even for tumors >5 cm
Favorable factors (multivariate): Younger age + tumor <4 cm → OS; extramedullary location + RT → DFS; RT + small tumor → LC
5-Year DFS: 50%
5-Year Local Control: 86%
5-Year Progression to MM: 45%; bone SP 51% vs. extramedullary SP 25%
Dose-response: No dose-response relationship for RT doses >30 Gy, even for tumors >5 cm
Favorable factors (multivariate): Younger age + tumor <4 cm → OS; extramedullary location + RT → DFS; RT + small tumor → LC
Adverse events
Main adverse events: Not systematically reported in this retrospective multicenter series. RT well tolerated across centers at median dose 40 Gy.
Conclusions
RT achieves 86% 5-year local control in solitary plasmacytoma. Progression to MM (45% at 5 years) is the main long-term failure mode. No dose-response relationship was found above 30 Gy, suggesting that 40 Gy is sufficient for most lesions and doses >50 Gy are unlikely to add benefit.
Key Limitations
Key Limitations: Retrospective multicenter design with heterogeneous patient selection and treatment; RT dose not standardized; no central pathology review; small EMP cohort; no modern staging (PET/CT, MRI whole-body) used in early accrual patients.
Clinical Context
One of the largest SP datasets in the literature. Establishes 40 Gy as appropriate standard dose — aligns with ILROG 2018 recommendation of 40–50 Gy. Key finding: no benefit from escalating beyond 30 Gy supports avoiding over-treatment. Extramedullary SP has significantly lower MM progression rate than bone SP, consistent with other series.
References