Lenalidomide and dexamethasone for Rosai-Dorfman disease: a single arm, single center, prospective phase 2 study.

Background: Rosai-Dorfman disease (RDD) is a rare heterogeneous histiocytic disorder lacking standardized first-line treatment. Methods: This single-center, phase 2 prospective study enrolled 13 newly diagnosed and 10 recurrent RDD patients from June 2021 to March 2023 at Peking Union Medical College Hospital (Beijing, China). Lenalidomide 25 mg days 1-21 plus dexamethasone 40 mg days 1, 8, 15, 22 was administered in 28-day cycles, totaling 12 cycles. The primary endpoint was progression-free survival (PFS). Secondary endpoints were overall response rate (ORR) to lenalidomide and dexamethasone (RD) regimen, toxicity, and overall survival (OS) measured from RD start to death or last follow-up. OS and PFS were estimated according to Kaplan-Meier survival analysis and compared with the log-rank test. For OS and OR rate, 95% confidence limits were obtained using the Clopper-Pearson method, with standard methods used for PFS. p < 0.05 was considered statistically significant. The trial was registered with ClinicalTrials.gov (NCT04924647). Findings: The median age was 44 years (IQR 35-54). All patients had extranodal RDD. MAPK pathway alterations occurred in 6/18 (33%). Elevated IL-6 and TNF-α were found in 39% (n = 9) and 70% (n = 16), respectively. All patients received ≥6 cycles (median 12, range 6-12, IQR 10-12). The ORR was 87% (20/23, 95% CI 66%-97%), 30% (n = 7) complete remission, 57% (n = 13) partial remission). Treatment with RD significantly decreased median serum levels of both IL-6 (from 5.9 (IQR 4.2-8.7) to 2.9 (IQR 2.1-5.9) pg/mL, p = 0.031) and TNF-α (from 12.2 (IQR 8.6-17.9) to 8.3 (IQR 6.1-10.5) pg/mL, p = 0.0012). With a median 26 months follow-up (range 6-28, IQR 16-28), 4 patients relapsed and none died. Two-year OS and PFS were 100.0% (95% CI 85%-100%) and 69.0% (95% CI 51%-94%), respectively. No grade 3-4 adverse events or discontinuations due to adverse events occurred. Twelve patients (n = 12, 52%) had grade 1-2 hematological toxicity. Other toxicities included constipation (n = 2, 9%), glucose intolerance (n = 2, 9%), edema (n = 2, 9%), insomnia (n = 1, 4%), and tremor (n = 1, 4%). Interpretation: Lenalidomide and dexamethasone regimen is an effective and safe regimen for newly diagnosed and recurrent RDD. Funding: National Natural Science Foundation of China, Beijing Natural Science Haidian frontier Foundation Funding, and the National High Level Hospital Clinical Research Funding.