Background
Retrospective single-institution analysis (MD Anderson Cancer Center) of 84 patients with solitary plasmacytoma (SP) treated with definitive RT from 1988–2008. 59 patients (70%) had bone SP, 25 (30%) had extramedullary SP. Serum paraprotein present in 39 patients (46%). Median RT dose 45 Gy.
Interventions and follow up
Arm A: Definitive RT for solitary plasmacytoma (bone or extramedullary); no randomizatio
Arm B: N/A — single-arm retrospective serie
Primary endpoint: Local control, progression to multiple myeloma, overall survival
mFollow up: Not specified (1988–2008 accrual)
Arm B: N/A — single-arm retrospective serie
Primary endpoint: Local control, progression to multiple myeloma, overall survival
mFollow up: Not specified (1988–2008 accrual)
Results
Local Control: 92% (77/84 patients)
5-Year OS: 78%; no difference between bone SP (76%) vs. extramedullary SP (85%), P=.274
5-Year Progression to MM: 47% overall; bone SP 56% vs. extramedullary SP 30%, P=.021
Serum paraprotein at diagnosis: MM progression 60% vs. 39% (P=.016)
RT dose and tumor size: Neither predicted local control
5-Year OS: 78%; no difference between bone SP (76%) vs. extramedullary SP (85%), P=.274
5-Year Progression to MM: 47% overall; bone SP 56% vs. extramedullary SP 30%, P=.021
Serum paraprotein at diagnosis: MM progression 60% vs. 39% (P=.016)
RT dose and tumor size: Neither predicted local control
Adverse events
Main adverse events: RT well tolerated at doses up to 53.4 Gy (range 36–53.4 Gy). Specific grade ≥3 toxicity rates not reported in this retrospective series. RT to spine or pelvis carries risk of myelosuppression in patients receiving systemic therapy.
Conclusions
Definitive RT achieves excellent local control (92%) in solitary plasmacytoma. Progression to MM remains the dominant long-term problem, occurring in ~47% at 5 years and significantly more often in bone SP than extramedullary SP. Serum paraprotein and bone location are adverse prognostic factors for MM progression.
Key Limitations
Key Limitations: Retrospective; heterogeneous RT doses and tumor sizes; long accrual period (20 years) with evolution in systemic therapy; small extramedullary SP cohort (n=25) limits subgroup analysis power; no defined RT dose standard evaluated prospectively.
Clinical Context
RT remains the standard definitive treatment for SP, with doses of 40–50 Gy recommended (ILROG 2018). Bone SP has substantially worse prognosis re: MM progression than extramedullary SP. Patients should be monitored indefinitely for MM development, as ~50% of bone SP eventually progress. The role of adjuvant bortezomib or lenalidomide post-RT is investigational.
References
References: Reed V et al, Cancer 2011 (PMID 21437886)