1084 - Solitary Plasmacytoma Treated by Lenalidomide and Dexamethasone in Combination with Radiation Therapy: Long Term Clinical Outcomes

Purpose/Objective(s):

Radiotherapy is the standard treatment for solitary plasmacytoma (SP), providing excellent local control but with a persistent risk of progression to multiple myeloma. The benefit of adding immunomodulatory agents to radiotherapy remains incompletely defined in the long term.

Materials/Methods:

We retrospectively analyzed 75 consecutive prospectively registered patients treated for histologically confirmed solitary plasmacytoma. All patients received normofractionated intensity-modulated radiotherapy (IMRT) with a median dose of 40.0 Gy (range, 20.0–46.0 Gy). Thirty-three patients (44.0%) received concurrent lenalidomide initiated on the first day of radiotherapy, while 42 patients (56.0%) were treated with radiotherapy alone. Survival outcomes were estimated using Kaplan-Meier methods and compared using log-rank tests. Univariate Cox proportional hazards models were performed. Endpoints included overall survival (OS), local recurrence-free survival (LRFS), multiple myeloma-free survival (MMFS), and progression-free survival (PFS).

Results:

With a median follow-up of 6.15 years, local control was excellent, with a 10-year LRFS of 91.2%. Estimated OS rates were 93.7% at 5 years and 90.4% at 10 years. Progression-free survival rates for the overall cohort were 72.6% at 3 years, 58.5% at 5 years, and 43.1% at 10 years, with a median PFS of 8.83 years. Concurrent lenalidomide was significantly associated with improved PFS in univariate analysis (HR = 0.315, 95% CI 0.128–0.775, p = 0.012); PFS rates were higher with lenalidomide than with radiotherapy alone at 5 years (71.8% vs 49.1%) and 10 years (71.8% vs 26.7%). In patients with solitary bone plasmacytoma (SBP, n = 65), this benefit was maintained, whereas no significant difference was observed in extramedullary plasmacytoma, likely due to limited sample size. A favorable but non-significant trend toward improved MMFS was observed with lenalidomide. No radiation-related grade =2 toxicity was reported. Lenalidomide-related toxicity occurred in 9.1% of patients, leading to treatment discontinuation in one case.

Conclusion:

IMRT provides durable local control and excellent long-term survival in solitary plasmacytoma. The addition of concurrent lenalidomide is safe and is associated with a significant improvement in progression-free survival, particularly in solitary bone disease. Larger prospective studies are warranted to confirm these findings.